The Palestinian militant group Hamas says it has chosen Yahya Sinwar, its top official in Gaza who masterminded the Oct. 7 attacks in Israel, as its new leader.

Hamas on Tuesday named Yahya Sinwar, its top official in Gaza who masterminded the Oct. 7 attacks in Israel, as its new leader in a dramatic sign of the power of the Palestinian militant group’s hardline wing after his predecessor was killed in a presumed Israeli strike in Iran.

The selection of Sinwar, a secretive figure close to Iran who worked for years to build up Hamas’ military strength, was a defiant signal that the group is prepared to keep fighting after 10 months of destruction from Israel’s campaign in Gaza and after the assassination of Sinwar’s predecessor, Ismail Haniyeh.