The new leader of the Islamic State, whose appointment the group announced on Thursday, is the brother of slain former caliph Abu Bakr al-Baghdadi, according to two Iraqi security officials and one western security source.

The Islamic State named its new leader Abu al-Hassan al-Hashemi al-Quraishi in a recorded audio message distributed online.

The announcement came weeks after the death last month of Abu Ibrahim al-Quraishi, the man who in turn succeeded Baghdadi in 2019 and became the group’s second so-called caliph. Both Baghdadi and Quraishi died by blowing themselves and family members up during US raids on their hideouts in northern Syria.

The Islamic State, a successor to al Qaida’s notoriously bloodthirsty Iraq branch, has its roots in an Islamist insurgency against US forces after they invaded Iraq and toppled Sunni dictator Saddam Hussein in 2003.

The Islamic State in its current form emerged from the chaos of the civil war in neighbouring Syria last decade and took over vast swathes of Iraq and Syria in 2014. Baghdadi declared an Islamic caliphate from a mosque in the northern Iraqi city of Mosul in 2014 and proclaimed himself caliph of all Muslims.

The Islamic State’s brutal rule, during which it killed and executed thousands of people in the name of its narrow interpretation of Islam, came to an end in Mosul when Iraqi and international forces defeated the group there in 2017.

Its remaining thousands of militants have in recent years mostly hid out in remote territory but are still able to carry out significant insurgent-style attacks.

One of the Iraqi security officials who spoke to Reuters on Friday said Badri had recently moved across the border from Syria, where he has been holed up, and into Iraq.

Badri will inherit control over financial resources that are significant, according to a report written in December by the UN sanctions monitoring team.

“Recent assessments ... put the group’s reserves at between $25 million and $50 million,” it said, but added that the Islamic State spends more than it earns, relying on “opportunistic extortion, looting and kidnap for ransom”.

Badri has two other brothers, one detained for years by Iraqi security services, the Iraqi security official said. The other brother's whereabouts is not known, but he is believed to be another Islamist radical, he said.