JERUSALEM (AP) — Israeli forces in Gaza killed Hamas’ top leader Yahya Sinwar, a chief architect of last year’s attack on Israel that sparked the war, the military said Thursday. Troops appeared to have run across him in a battle, only to discover afterwards that a body in the rubble was the man Israel has hunted for more than a year.

Sinwar has topped Israel’s most wanted list since the beginning of the Israel-Hamas war just over a year ago, and his killing strikes a powerful blow to the militant group. There was no immediate confirmation from Hamas of his death.

The military confirmed Sinwar’s death after conducting DNA tests on a body it said was among three militants killed Wednesday during operations in Gaza. Foreign Minister Israel Katz called Sinwar’s killing a “military and moral achievement for the Israeli army,” saying it would “create the possibility to immediately release the hostages.”

Defense Minister Yoav Gallant addressed Hamas fighters, saying it “is time to go out, release the hostages, raise your hands, surrender.”

Sinwar was one of the chief architects of Hamas’ attack on Israel on Oct. 7, 2023, and Israel has vowed to kill him since the beginning of its retaliatory campaign in Gaza. He has been Hamas’ top leader inside the Gaza Strip for years, closely connected to its military wing while dramatically building up its capabilities.

An Israeli security official said it appeared that the man who turned out to be Sinwar was killed in a battle, not in a planned targeted airstrike.

Photos circulating online showed the body of a man resembling Sinwar with a gaping head wound, dressed in a military-style vest, half buried in the rubble of a destroyed building. The security official confirmed the photos were taken by Israeli security officials at the scene. The official spoke on condition of anonymity because of the ongoing investigation.

The Israeli news site N12 said Sinwar appears to have been killed by chance in a battle on Wednesday. It said that troops tracked a group of militants into a building, then attacked the militants with tank fire, causing the building to collapse. As troops unearthed the dead militants, they noticed that one appeared to resemble Sinwar.

Sinwar was imprisoned by Israel from the late 1980s until 2011, and during that time he underwent treatment for brain cancer – leaving Israeli authorities with extensive medical records.

President Joe Biden has been briefed on Israel’s investigation into whether it killed Sinwar, and U.S. officials have been in close contact with Israeli officials throughout Thursday morning, according to a senior administration official.

Sinwar was chosen as Hamas’s top leader in July after his predecessor, Ismail Haniyeh, was assassinated in an apparent Israeli strike in the Iranian capital Tehran. Israel has also claimed to have killed the head of Hamas’ military wing Mohammed Deif in an airstrike, but the group has said he survived.

The report of his death came as Israeli forces continued a more than week-old major air and ground assault in the Jabaliya refugee camp in northern Gaza. On Thursday, an Israeli strike hit a school sheltering displaced Palestinians, killing at least 28 people, according to Gaza’s Health Ministry.

Fares Abu Hamza, head of the Gaza Health Ministry’s emergency unit in the north, said the dead included a woman and four children, correcting an earlier report of five children. He said dozens of people were wounded.

The Israeli military said it targeted a command center run by Hamas and Islamic Jihad inside the school. It provided a list of around a dozen names of people it identified as militants who were present when the strike was called in. It was not immediately possible to verify the names.

Israel has repeatedly struck tent camps and schools sheltering displaced people in Gaza. The Israeli military says it carries out precise strikes on militants and tries to avoid harming civilians, but its strikes often kill women and children.

Israel launched its campaign in Gaza to eliminate Hamas after the militants stormed into southern Israel on Oct. 7, 2023, killing some 1,200 people, mostly civilians, and abducting around 250 others. Some 100 captives are still inside Gaza, about a third of whom are believed to be dead.

Israel’s offensive has killed over 42,000 Palestinians, according to Gaza’s Health Ministry. It does not differentiate between civilians and combatants but says women and children make up a little more than half of the fatalities.

Northern Gaza was the first target of Israel’s ground invasion nearly a year ago and has suffered the heaviest destruction of the war, with entire neighborhoods in Gaza City and other towns reduced to rubble. Most of the population fled after Israel issued evacuation orders in the opening days of the war, but about 400,000 are believed to have remained despite the harsh conditions.

Earlier this month, Israel once again ordered the full-scale evacuation of the north, and allowed no food aid to enter the area for around two weeks. That led many Palestinians to fear that it had adopted a surrender-or-starve strategy suggested by former Israeli generals.

Israel allowed two shipments of aid to enter the north earlier this week after the United States warned it might reduce its military aid if its ally did not do more to address the humanitarian crisis.

Since the start of the conflict, Israeli forces have launched repeated operations into Jabaliya, a densely populated urban refugee camp dating back to the 1948 war surrounding Israel’s creation. The military says militants have repeatedly regrouped there after major operations.