In an announcement by the Islamic State’s propaganda arm, the group also confirmed that its former spokesman, Abu al-Hassan al-Muhajir, had been killed, which happened in a separate strike after Mr. al-Baghdadi’s death.

The Islamic State’s announcement was reported on the Twitter account of the Site Intelligence Group, which monitors the online content of the Islamic State and other extremist militant groups.

The announcement said Mr. al-Baghdadi had been succeeded as the Islamic State’s leader by Ibrahim al-Hashemi al-Qurayshi, whom it identified as the “emir of the believers” and “caliph.” Mr. al-Qurayshi appeared to be largely unknown, at least outside the ranks of the organization.