President Joe Biden said Sunday that the U.S. “shall respond” after three American troops were killed and dozens more were injured in an overnight drone strike in northeast Jordan near the Syrian border. Biden blamed Iran-backed militias for the first U.S. fatalities after months of strikes by such groups against American forces across the Middle East since the start of the Israel-Hamas war.

Biden, who was traveling in South Carolina, asked for a moment of silence during an appearance at a Baptist church's banquet hall.

“We had a tough day last night in the Middle East. We lost three brave souls in an attack on one of our bases," he said. After the moment of silence, Biden added, “and we shall respond.”

With an increasing risk of military escalation in the region, U.S. officials were working to conclusively identify the precise group responsible for the attack, but they have assessed that one of several Iranian-backed groups was behind it.

Biden said in a written statement that the United States “will hold all those responsible to account at a time and in a manner (of) our choosing.” Defense Secretary Lloyd Austin said "we will take all necessary actions to defend the United States, our troops, and our interests.”

Iran-backed fighters in east Syria began evacuating their posts, fearing U.S. airstrikes, according to Omar Abu Layla, a Europe-based activist who heads the Deir Ezzor 24 media outlet. He told The Associated Press that the areas are the strongholds of Mayadeen and Boukamal.

According to a U.S. official, the number of troops injured by the one-way attack drone rose to at least 34. Another official, who also spoke on condition of anonymity to discuss details not made public, said a large drone struck the base, which two other American officials identified as an installation in Jordan known as Tower 22. It is along the Syrian border and is used largely by troops involved in the advise-and-assist mission for Jordanian forces.

The small installation, which Jordan does not publicly disclose, includes U.S. engineering, aviation, logistics and security troops. Austin said the troops were deployed there “to work for the lasting defeat of ISIS.” Three officials said the drone struck near the troops' sleeping quarters, which they said explained the high casualty count.

The U.S. military base at al-Tanf in Syria is just 20 kilometers (12 miles) north of Tower 22. The Jordanian installation provides a critical logistical hub for U.S. forces in Syria, including those at al-Tanf, which is near where the borders of Iraq, Syria and Jordan intersect.

In a statement on Jordan’s state-run Petra news agency, the country “condemned the terrorist attack” that targeted the U.S. troops. That report described the drone strike as targeting “an outpost on the border with Syria” and said it did not wound any Jordanian troops.

“Jordan will continue to counter terrorism and the smuggling of drugs and weapons across the Syrian border into Jordan, and will confront with firmness and determination anyone who attempts to attack the security of the kingdom,” the statement attributed to Muhannad Mubaidin, a government spokesman, said.

U.S. troops long have used Jordan, a kingdom bordering Iraq, Israel, the Palestinian territory of the West Bank, Saudi Arabia and Syria, as a basing point. Some 3,000 American troops typically are stationed across Jordan, but the number at Tower 22 wasn’t immediately known and isn’t routinely disclosed.

Since the war in Gaza began Oct. 7, Iranian-backed militias have struck American military installations in Iraq more than 60 times and in Syria more than 90 times, with a mix of drones, rockets, mortars and ballistic missiles. The attack Sunday was the first targeting American troops in Jordan during the Israel-Hamas war and the first to result in the loss of American lives. Scores of U.S. personnel have been wounded, including some with traumatic brain injuries, during the attacks.

The militias have said that their strikes are in retaliation for Washington’s support for Israel in the war in Gaza and that they aim to push U.S. forces out of the region.

The U.S. in recent months has struck targets in Iraq, Syria and Yemen to respond to attacks on American forces in the region and to deter Iran-backed Houthi rebels from continuing to threaten commercial shipping in the Red Sea.

“I am confident the Biden Administration will respond in a deliberate and proportional manner,” said Sen. Jack Reed, D-R.I., who heads the Senate Armed Services Committee.

Republicans in Congress said the administration's approach had failed to deter America's adversaries in the region.

“We need a major reset of our Middle East policy to protect our national security interests,” said Republican Rep. Michael McCaul of Texas, chairman of the House Foreign Affairs Committee. Sen. Lindsay Graham, R-S.C., went further, urging the administration “to strike targets of significance inside Iran, not only as reprisal for the killing of our forces, but as deterrence against future aggression. The only thing the Iranian regime understands is force.”

Biden, who was in Columbia, South Carolina, on Sunday, was briefed in the morning by Austin, national security adviser Jake Sullivan, and principal deputy national security adviser Jon Finer, White House press secretary Karine Jean-Pierre said. In the afternoon, he met virtually with Vice President Kamala Harris and his national security team for an update.

The president, in the written statement, called it a “despicable and wholly unjust attack” and said the service members were “risking their own safety for the safety of their fellow Americans, and our allies and partners with whom we stand in the fight against terrorism. It is a fight we will not cease.”

Syria is still in the midst of a civil war and long has been a launch pad for Iranian-backed forces there, including the Lebanese militia Hezbollah. Iraq has multiple Iranian-backed Shiite militias operating there as well.

Jordan, a staunch Western ally and a crucial power in Jerusalem for its oversight of holy sites there, is suspected of launching airstrikes in Syria to disrupt drug smugglers, including one that killed nine people earlier this month.

An umbrella group for Iran-backed factions known as the Islamic Resistance in Iraq earlier claimed launching explosive drone attacks targeting three areas in Syria, as well as one inside of “occupied Palestine.” The group has claimed responsibility for dozens of attacks against bases housing U.S. troops in Iraq and Syria since the Israel-Hamas war began.

Three officials with Iran-backed militias in Iraq, who spoke on condition of anonymity because they were not authorized to discuss the matter with journalists, said the drone attack against the base in Jordan was launched by one of the Iraqi groups. No faction has yet officially claimed responsibility.

Officials said the U.S. military is not tracking any other attacks on its forces Sunday in the region.

Drone Attack In Jordan Kills Three American Troops 

Three U.S. troops were killed and more than two dozen injured by an Iranian-backed militia drone strike on Tower 22.

In a major escalation of tensions in the Middle East, three U.S. troops were killed and more than two dozen injured by a drone attack on a U.S. base in Jordan near the border with Syria on Jan. 28, according to U.S. Central Command. This attack marked the first time U.S. troops were killed in the Middle East since the beginning of the ongoing Israel-Hamas war on Oct. 7. It is also the first attack on American troops in Jordan since that conflict erupted.

President Joe Biden and Defense Secretary Lloyd Austin blamed the attack on Iranian-backed militia groups. "We will hold all those responsible to account at a time and in a manner our choosing," said Biden. Austin later echoed that sentiment in a statement of his own.

CENTCOM did not say who launched the drones, or name the branch of the troops killed and injured. The Islamic Resistance, a loose-knit group of Iranian-backed militias, said that it attacked three U.S. bases in Syria, including Al Tanf as well as the Israeli Zevulun naval facility in the port of Haifa.

"The Islamic Resistance confirms that it will continue to destroy enemy strongholds," said the group, threatening additional attacks.

The attack in Jordan took place at a small U.S. logistics hub called Tower 22 that serves the Al-Tanf base in Syria, The Wall Street Journal reported. Located about 12 miles south of Al Tanf, it is used largely by troops involved in the advise-and-assist mission for Jordanian forces, The Associated Press reported. The small installation, which Jordan does not publicly disclose, includes U.S. engineering, aviation, logistics and security troops.

The number of troops wounded may grow, according to a U.S. official cited by the AP. The official, who spoke on condition of anonymity to discuss details not made public, said a large drone struck the base.

"It’s unclear why air defenses failed to intercept the drone, which appears to be the first known attack on Tower 22 since attacks on U.S. and coalition forces began on October 17. U.S. forces at the outpost are there as part of an advise-and-assist mission with Jordan," CNN reported.

Some 3,000 American troops typically are stationed in Jordan, the AP noted, adding that Iranian-backed militias have struck American military installations in Iraq more than 60 times and in Syria more than 90 times, with a mix of drones, rockets, mortars and ballistic missiles.

That includes a massive attack by Iranian-made ballistic missiles on the Al-Assad Air Base in Iraq on Jan. 20 that inflicted traumatic brain injuries on several troops.

Previous attacks have wounded scores of U.S. personnel, including some with traumatic brain injuries.

Biden and Vice President Kamala Harris were briefed by their national security team this afternoon by National Security Advisor Jake Sullivan, Secretary Antony Blinken, Secretary Lloyd J. Austin III, Chairman CQ Brown, Director Avril Haines, Director Bill Burns, Ambassador Linda Thomas Greenfield, Principal Deputy National Security Advisor Jon Finer, and Chief of Staff Jeff Zients.

Austin, in his own statement, said he is "outraged."

“I am outraged and deeply saddened by the deaths of three of our U.S. service members and the wounding of other American troops in an attack last night against U.S. and Coalition forces, who were deployed to a site in northeastern Jordan near the Syrian border to work for the lasting defeat of ISIS," Austin remarked. "These brave Americans and their families are in my prayers, and the entire Department of Defense mourns their loss."

"Iran-backed militias are responsible for these continued attacks on U.S. forces, and we will respond at a time and place of our choosing. The President and I will not tolerate attacks on American forces, and we will take all necessary actions to defend the United States, our troops, and our interests.”

Iran-backed fighters in east Syria began evacuating their posts, fearing U.S. airstrikes, according to Omar Abu Layla, a Europe-based activist who heads the Deir Ezzor 24 media outlet, AP reported. Layla told the AP that the areas are the strongholds of Mayadeen and Boukamal. Those sites are located about 150 miles northeast of where the U.S. base in Jordan was hit.

The U.S. has carried out a number of strikes against Iranian-backed militias, including one Jan. 20 in response to the attack on Al-Assad.

Update: 4:16 PM Eastern -

Jordan issued a statement condemning the attack and said none of its troops were hurt:

"Jordan condemned the terrorist attack that targeted an outpost on the border with Syria, killing three US soldiers and injuring two others from the US forces that are cooperating with Jordan in countering terrorism and securing the border."

"Minister of Government Communications and government spokesperson, Muhannad Mubaideen, expressed Jordan's condolences to the United States over the victims of the attack, which was carried out by a drone, and wished the injured a speedy recovery."

"Mubaideen said that the terrorist attack did not result in any casualties among officers of the Jordan Armed Forces."

"He stressed that Jordan will continue to counter terrorism and the smuggling of drugs and weapons across the Syrian border into Jordan, and will confront with firmness and determination anyone who attempts to attack the security of the Kingdom."

"Jordan had previously announced that it is cooperating with its partners to secure the border and has asked the United States and other friendly countries to provide it with the military systems and equipment necessary to increase its capabilities to secure the border and face the dangers across it."

Tower 22 is about 145 miles northeast of Jordan's Muwaffaq Salti Air Base. As we have previously reported, "it is a major staging location for U.S. airpower and a critical intrathreater transit hub for American forces, and has been in especially heavy use since the current Israel-Gaza conflict erupted. A Patriot battery is likely desired to protect this shared air base."

"The forward operating base in At Tanf in Syria, which sits in a tri-border region opposite northeastern Jordan and southwestern Iraq, has been a top target of attacks from Iranian-backed proxies, as well. It has come under sporadic attack for the better part of a decade, but in recent weeks, it has been the focus of drone and rocket strikes. A Patriot battery located across the border near the border in Jordan could cover At Tanf as a contingency against wider-scale attacks should the conflict erupt throughout the reason. A shield against Iranian ballistic missiles would be of particular need."

Drone strike kills 3 US troops. Here's how Arizona's congressional delegation responded.

Three U.S. service members were killed and dozens wounded Sunday in a drone attack by "Iran-backed militants" at a U.S. base along the Jordanian-Syrian border as the war in Gaza shows signs of spreading across the region.

They are the first U.S. troops killed by enemy fire in the Middle East since Hamas-led militants attacked Israel on Oct. 7, igniting the war that has led to more than 26,000 Palestinian deaths in Gaza. Identities of the service members will be withheld until 24 hours after their families have been notified, U.S. Central Command said.

President Joe Biden issued a statement saying an investigation was underway and that "we know it was carried out by radical Iran-backed militant groups" operating in Syria and Iraq. The three were "patriots in the highest sense" and the nation is grieving, he said.

Several congressional Arizona leaders issued swift responses to the drone attack on Sunday. Here is a roundup of what they had to say:

U.S. Sen. Kyrsten Sinema, I-Ariz.

"Last night, an Iranian-backed militia group carried out a drone attack that killed 3 U.S. servicemembers and wounded more in Jordan. I join all Arizonans in mourning the loss of these brave heroes and wishing the injured troops a quick and full recovery.

As we await further details, we stand unflinching in our mission to defeat this heinous terrorism. We’re sending strength and gratitude to the families of those killed and injured during this extraordinarily difficult time."

U.S. Sen. Mark Kelly, D-Ariz.

"Three servicemembers made the ultimate sacrifice and 25 more were injured in service of our country. I'm thinking of them and their loved ones. This attack is a dangerous escalation by Iran's proxies. Those responsible must be held accountable."

U.S. Rep. Ruben Gallego, D-Ariz.

U.S. Rep. Ruben Gallego called for the drone attack carried out by "Iranian-backed militants" that killed three American troops to "not go unpunished" on Sunday.

“I am grieving for the families of the three service members killed in Jordan. The attack carried out by Iranian-backed militants is a heinous escalation, and it must not go unpunished," Gallego said in a statement.

Gallego said he was committed to providing the administration with the needed resources to protect U.S. troops in the region and "hold Iran accountable.”

U.S. Rep. Juan Ciscomani, R-Ariz.

"Laura & I are deeply saddened to hear of the deaths of 3 servicemembers in Jordan and praying for those injured in the attacks. The growing aggression from Iran-backed proxies and other adversaries must be squashed with a swift response from the United States."

U.S. Rep. Andy Biggs, R-Ariz.

"My prayers go out to the US service members who were killed and injured by an Iran-backed drone attack in Jordan. 3 patriots died while 25 more were injured. Joe Biden has emboldened Iran and shown weakness on the global stage. We have to have a stronger Commander-in-Chief."

U.S. Rep. Greg Stanton, D-Ariz.

"My heart goes out to the loved ones of the three American servicemembers killed—and to all those injured—while bravely serving our nation. The U.S. must hold Iran and its proxies accountable."