Israeli forces in Gaza killed Hamas 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 unknowingly in a battle,

The Israeli military confirmed that Yahya Sinwar, the leader of Hamas, was killed on Wednesday. His body was identified by the Israeli authorities, the military said.

Sinwar — who had been the de facto head of Hamas since Ismail Haniyeh was killed in July — was a U.S.-designated terrorist and had been at the top of Israel’s most-wanted list since the start of the Israel-Hamas war a year ago.