After Hamas gunmen stormed into 85-year-old Yocheved Lifshitz's house and shot her husband in the hand, they threw her on a motorbike and dragged her off to a tunnel network beneath Gaza, her grandson Daniel says.

Freed Israeli hostage Yocheved Lifshitz, 85, takes part in a protest outside the defence ministry in Tel Aviv.

It was in the "very damp", "very deep" warren of subterranean rooms and passages that his grandmother -- now released -- told family she had encountered someone few Israelis have for years: Yahya Sinwar, the head of Hamas in Gaza and a mastermind of the October 7 attacks.

"She said she saw him, and told him: 'How are you not ashamed? How are they not ashamed to do such things to people who fought for peace their entire lives?'" her grandson told AFP in Tel Aviv.

"And she said he stayed quiet."

But her son Izhar Lifshitz said it was unlikely his mother had actually met one of Israel's most wanted men, saying it was likely she had talked with another "senior figure within Hamas".

"After the security officials questioned her and showed her photos, it turned out she didn't meet Sinwar. There are many Hebrew speakers with beards who speak and look like Sinwar," he told Israel's Channel 13 television.

"She had a meeting with a senior figure within Hamas. She thought she was speaking with Yahya Sinwar and that's what she told us when she came back but after it was checked, it turns out it wasn't him."

Hamas officials declined to comment.

Known for his secrecy as well as his commitment to armed struggle, Sinwar learned near-perfect Hebrew during the years he spent in Israeli prisons.

A founding member of Hamas, he was a commander in its armed wing, and once led efforts to flush out and mercilessly punish Palestinians accused of collaborating with Israel. He was elected Hamas' Gaza leader in 2017.

Lifshitz was released in late October along with another elderly woman hostage, but her husband Oded, 83, remains in captivity.

Hamas said the pair were freed for humanitarian reasons, and Lifshitz said their captors had been "courteous" and "treated us well", organising doctor's visits every few days.

But her grandson said she'd nearly died in captivity.

"She got a stomach infection there, she lost almost 10 kilos (22 pounds), she would have died if she had stayed there."

After Friday's collapse of a truce underpinning a hostage-prisoner exchange deal and the resumption of fierce fighting in Gaza, the fate of the remaining hostages remains unclear.

Yocheved told the family she had not seen her husband since both of them were taken hostage on October 7.

"My grandmother's last glimpse of him was while she was on the motorcycle," Daniel told AFP, saying they had been married for 63 years.