Iran-backed Hizbollah trained Hamas in Syria and Lebanon, it was claimed on Friday, as the United States embarked on high-stakes shuttle diplomacy to prevent war in the Middle East.

Hamas terrorists were trained in Syria to raid Israeli homes and take civilians hostage, while the men who carried out the paraglider attacks were trained in Lebanon, the New York Times reported.

The claims by two Iranian sources highlight the scale of the challenge faced by Antony Blinken, the US secretary of state, in treading a fine line between backing Israel and convincing Arab countries to show restraint.

Lebanon’s Hizbollah movement said on Friday it would be “fully prepared” to join its Palestinian ally Hamas in the war against Israel when the time was right.

Mr Blinken has begun a tour of the US’s Arab allies, including Saudi Arabia, Jordan, Qatar, the United Arab Emirates and Egypt, in the hope of stopping the region tipping into a wider conflict.

The frantic diplomacy, which comes after calls from Joe Biden, the US president, is aimed at ensuring the Gulf states keep their domestic Islamist groups under control as Israel strikes Gaza.

On Thursday in Tel Aviv, Mr Blinken urged Israel to ensure civilians in Gaza were protected before travelling to the six Arab nations.

He said he wanted to convince them to use their “leverage” with Hamas to unconditionally and immediately free an estimated 150 Israeli hostages.

Swelling anger

In a bid to keep a lid on swelling Arab anger, Mr Blinken had discussed how to set up safe zones for citizens in Gaza after Israel told more than one million people to evacuate ahead of an expected ground invasion.

“The Israelis are committed to it,” a US official told reporters on Mr  Blinken’s plane.

Earlier efforts to let Gazans flee to adjacent Egypt failed in the face of a lack of support.

King Abdullah II of Jordan told Mr Blinken: “The crisis should not be spread to neighbouring countries.”

The long-time US ally called for “humanitarian corridors” to bring relief into Gaza and de-escalate the situation. Abdullah, whose kingdom is home to two million Palestinian refugees, warned against another refugee crisis, this time from Gaza.

Mr Blinken discussed “ways to address the humanitarian needs of civilians in Gaza while Israel conducts legitimate security operations to defend itself from terrorism,” a US spokesman said.

He also met with Mahmoud Abbas, the Palestinian president, in Amman, the capital of Jordan. Mr Abbas, 88, is a sworn foe of Hamas, whose control of the Gaza Strip has led to a 17-year Israeli blockade.

Mr Blinken praised Mr Abbas for efforts to maintain calm in the West Bank over the past week

The Palestinian Authority enjoys small levels of autonomy in the West Bank but Benjamin Netanyahu, the Israeli prime minister, has long sought to sideline Mr Abbas.

The US chief diplomat then headed to Qatar, which blamed Israel for the Hamas terror attack, He will later travel to Bahrain, Saudi Arabia, the United Arab Emirates and Egypt.

Momentum behind the US-led diplomacy to normalise relations between Saudi Arabia and Israel - a landmark step for the conservative kingdom that is guardian of Islam’s two holiest sites - is now feared to be lost.

Saudi Arabia is historically a vital financial supporter of the Palestinian Authority but it has no links to Hamas, which is backed by its rival Iran.

Washington is concerned Iran could try to capitalise on the current conflict by unleashing Hizbollah or using proxies from Gaza to Lebanon, Iraq and Syria to attack Gulf Arabs.

Hossein Amir-Abdollahian, Iran’s Foreign Minister, warned on Friday during a visit to Beirut that new fronts could open if Israel continues its “war crimes and humanitarian siege on Gaza”.

Iranian denial

Ayatollah Ali Khamenei, Iran’s supreme leader, has denied Tehran played a role in the terror attack.

“We kiss the foreheads and arms of the resourceful and intelligent designers,” Mr. Khamenei said but added: “Those who say that the recent saga is the work of non-Palestinians have miscalculated.”

That is unlikely to convince an enraged Israel.

Yoav Gallant, its defence minister, said Hamas was part of  an “axis of evil” with Iran.

Asked at a press conference with Lloyd Austin, his US counterpart, if Tehran ordered the attack, he said: “It doesn’t matter ... the idea is an Iranian idea.”