The Islamic State group is mourning the death of its leader Abu Bakr al-Baghdadi and has announced a successor in a new audio release.

The group identified the new leader as Abu Ibrahim al-Hashimi in the audio released Thursday by the IS central media arm, al-Furqan Foundation.

The speaker in the audio also confirmed the death of Abu Hassan al-Muhajir, a close aide of al-Baghdadi and a spokesman for the group.

Al-Muhajir was killed in a joint US operation with Kurdish forces in Jarablus, in northern Syria on Sunday, hours after al-Baghdadi blew himself up during a US raid in Syria's northwestern Idlib province.

The speaker named Abu Hamza al-Qurashi urged followers to pledge allegiance to the new Caliph and addressed the Americans saying; "Don't rejoice."