BEIRUT, Lebanon — A day after an American raid killed Islamic State leader Abu Bakr al-Baghdadi, a separate attack killed the man who was considered his likely successor, according to the leader of a Syrian Kurdish militia and a Syrian activist.
The spokesman, known by his nom de guerre Abu Hassan al-Muhajir, was being smuggled across northern Syria in the back of an oil tanker truck when it was hit by what witnesses said they believed to be an American airstrike, according to Hussein Nasser, an activist who said he had spoken to people at the scene.
Mazlum Abdi, the head of a Kurdish-led militia that fought the Islamic State with the United States, wrote on Twitter that Mr. al-Muhajir had been killed on Sunday in an operation coordinated between his forces and the United States.
American officials could not immediately confirm the reports that Mr. al-Muhajir had been killed.
The spokesman issued his last statement in March, calling for retaliation for the killing of 50 Muslims in New Zealand by a white supremacist.
Little is known about him, including his real name and nationality, complicating efforts to confirm that he was the one killed in Sunday’s strike. But terrorism experts considered him a possible successor to Mr. al-Baghdadi.
Ben Hubbard reported from Beirut, and Karam Shoumali from Berlin