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

The choice of Sinwar, a secretive figure who leads Hamas's hard-liners and is close to Iran, was a defiant step. Sinwar is at the top of Israel's kill list as it seeks to destroy Hamas and its leadership after the Oct. 7 attacks, in which militants killed 1,200 people in southern Israel and took about 250 as hostages, according to Israeli tallies.

Hamas said in a statement it named Sinwar as the new head of its political bureau to replace Ismail Haniyeh, who was killed in Iran last week in a presumed Israeli strike. Also last week, Israel said it had confirmed the death of the head of Hamas's military wing, Mohammed Deif, in a July airstrike in Gaza. Hamas has not confirmed his death.

Unlike Haniyeh, who had lived in exile in Qatar for years, Sinwar has remained in Gaza. As Hamas's leader in the territory since 2017, he rarely appeared in public, but kept an iron grip on Hamas's rule. Close to Deif and the armed wing, known as the Qassam Brigades, Sinwar worked to build up the group's military capabilities.

Sinwar has been in deep hiding since the Oct. 7 attacks, while Israel unleashed its campaign in Gaza and the death toll among Palestinians — now near 40,000, according to the Gaza health ministry — continues to rise.