Palestinian militant group Hamas on Friday confirmed its leader Yahya Sinwar had been killed, a day after Israel announced his death in Gaza.

"We mourn the great leader, the martyred brother, Yahya Sinwar, Abu Ibrahim," Qatar-based Hamas official Khalil al-Hayya said in a recorded video statement broadcast by Al Jazeera.

Sinwar became Israel's most wanted man after the October 7, 2023 attack, the deadliest in Israeli history.

Israel announced Sinwar's death on Thursday, which Prime Minister Benjamin Netanyahu called a "heavy blow" to the Palestinian group Israeli forces have been fighting in Gaza more than a year.

Hamas's October 7 attack resulted in the deaths of 1,206 people, mostly civilians, according to an AFP tally of official Israeli figures that includes hostages killed in captivity.

Militants also took 251 people hostage during the attack. Ninety-seven remain in Gaza, including 34 who Israeli officials say are dead.

In his statement, Hayya said Hamas would not release the captives until the war in Gaza ends.

The hostages "will not return... unless the aggression against our people in Gaza stops," the senior Hamas official said.

He called on Israel to withdraw from Gaza and release Palestinian prisoners held in Israeli jails.

Israel's campaign to crush Hamas and bring back the hostages seized by militants has killed 42,500 people in Gaza, the majority civilians, according to data from the health ministry in the Hamas-run territory, figures which the UN considers reliable.

Hayya said the militant group would take strength from Sinwar's killing, which he said has set him among "the leaders and symbols of the movement who preceded him".

Directing the fighting in the Palestinian territory as its Gaza leader throughout the war, Sinwar was named the movement's overall chief in August, after the death of Hamas's political bureau chief Ismail Haniyeh, who was assassinated in Tehran on July 31.

Sinwar had not been seen in public since the October 7 attack, and Israeli commanders believed he hid in a labyrinthine maze of tunnels that Hamas built under the Gaza Strip over the years.