Iranian authorities confirmed on Tuesday that Ali Larijani, a senior security official and a leading figure among the conservative faction in Iran’s theocratic government, was killed in an attack in Israel. He was 67 years old.

It was widely believed that Larijani was effectively ruling Iran following the death of Iran’s supreme leader. He was appointed by Ayatollah Ali Khamenei to advise on the strategy for nuclear negotiations with the Trump administration and traveled to Oman two weeks before the war began to meet with mediators. Like other senior Iranian leaders, Larijani is subject to severe U.S. sanctions and is suspected of involvement in the violent crackdown on mass protests in January.

After Khamenei’s death, he is ineligible to become Supreme Leader because he is not a Shiite cleric. However, it is widely expected that he will serve as a top advisor.