US President Joe Biden said Saturday that the body of Israeli-American hostage Hersh Goldberg-Polin was among six recovered in Gaza by Israeli forces.

"Earlier today, in a tunnel under the city of Rafah, Israeli forces recovered six bodies of hostages held by Hamas," Biden said in a statement.

"We have now confirmed that one of the hostages... was an American citizen, Hersh Goldberg-Polin," the president added.

The 23-year-old was among 251 hostages seized during the October 7 attack on southern Israel by Palestinian militants.

Around 100 hostages remain in captivity, dozens of whom the Israeli military says are dead.

The parents of Goldberg-Polin, who was abducted from the Supernova music festival, addressed delegates at the Democratic National Convention in Chicago last month.

On Thursday, the couple joined other relatives of hostages rallying near the Gaza border.

"Hersh! It's Mom... I love you, stay strong, survive," Rachel Goldberg-Polin shouted into a microphone.

Her son had hidden in a bomb shelter with other people on October 7 but it was surrounded by gunmen, who attacked it with grenades.

A Hamas video from the day showed him being loaded onto a pick-up truck with part of his left arm, which was blown off in the attack, missing.

He appeared in a proof-of-life video released by Hamas on April 24 in which he said the captives were living "in hell". His left arm had been amputated below the elbow.

Hamas's October 7 attack resulted in the deaths of 1,199 people, mostly civilians, according to an AFP tally based on Israeli official figures.

Israel's retaliatory military campaign has killed at least 40,691 people in Gaza, according to the territory's health ministry. The UN rights office says most of the dead are women and children.