The so-called Islamic State (IS) confirmed on Thursday that its leader Abu Bakr al-Baghdadi had been killed in a weekend raid by the US special forces in northwestern Syria — and vowed revenge against the US.

Axar.az reports citing EuroNews that the group confirmed its leader's death in an audiotape posted online and said a successor, who's been identified as Abu Ibrahim al-Hashemi al-Quraishi, had been named.

Aymenn al-Tamimi, a researcher at Swansea University focusing on Islamic State, told that the new leader was not very well known. A spokesman for the terror group also threatened the US with retaliation for the killing of its leader.

Baghdadi's death is likely to cause Islamic State to splinter, leaving whoever emerged as its new leader with the task of pulling the group back together as a fighting force, analysts told Reuters.

It remains to be seen whether the loss of its leader will affect the group's capabilities. But even if it faces difficulties in the transition, the underlying ideology and the sectarian hatred it promoted remain attractive to many, they said. IS also confirmed the death of its spokesman Abu al-Hassan al-Muhajir.

"I think they're trying to send the message, 'Don't think you've destroyed the project just because you've killed Abu Bakr al-Baghdadi and the official spokesman'," Tamimi said.

"ISIS is trying to show its followers it respects that tradition, but Muslims more widely aren't likely to care very much, considering the wide violations of the Islamic law that ISIS has clearly engaged with," Hellyer added.