A Syrian boy walks on February 3, 2022 at the scene following an overnight raid by US special operations forces against suspected jihadists in Atme, in Syria s northwestern province of Idlib which left at least nine people dead, including three civilians. (AFP)
The announcement came more than a month after the IS chief died during a US raid that saw troops flown by helicopter into northwest Syria, in an area controlled by rival jihadists.
IS personnel have "pledged allegiance" to "Abu Hasan al-Hashemi al-Qurashi as an emir over believers and the caliph of Muslims," the group's spokesperson said in an audio recording released on its social media channels.
The recording confirmed the death of the former IS chief along with the group's ex-spokesman.
"Abu Ibrahim al-Qurashi and the official Islamic State group spokesman... Abu Hamza al-Qurashi... were killed in recent days," said the new spokesperson, identified as Abu-Omar al-Muhajjir.
Little is known about the new leader, who will serve as the group's third chief since it's inception.
According to the White House and US defence officials, Abu Ibrahim al-Hashimi al-Qurashi died when he detonated a bomb to avoid capture.
His demise, on February 3 in the town of Atme, was the biggest setback to IS since his own predecessor, the better-known Abu Bakr al-Baghdadi, was killed in a US commando raid in the same Syrian region of Idlib in 2019.
According to the IS audio statement, Abu Hasan al-Qurashi was endorsed by Abu Ibrahim before his death and had his appointment has been confirmed by the group's senior leaders.
The recording did not offer further details.
Abu Hasan al-Qurashi rises to the helm at a time when the group has been weakened by US-backed operations in Iraq and Syria aiming to thwart a jihadist resurgence.
IS' self-declared caliphate, established from 2014, once stretched across vast parts of Syria and Iraq and administered millions of inhabitants.
A long and deadly military fightback led by Kurdish-Syrian and Iraqi forces with backing from the United States and other powers eventually defeated the jihadist proto-state in March 2019.
The remnants of IS in Syria mostly went to desert hideouts from which they continue to harass Kurdish-led forces and Syrian government troops.
The jihadists also continue to mount attacks in Iraq from hideouts there.
A UN report last year estimated that around 10,000 IS fighters remained active across the two countries.
Abu Ibrahim al-Qurashi's death in February came two weeks after IS launched an attack on a northeast Syria prison housing fellow jihadists.
The jail break attempt from the sprawling Ghwayran complex in the northeastern city of Hasakeh triggered a week of clashes inside and around the facility, leaving hundreds dead.
But hundreds of IS prisoners, including senior leaders, are thought to have escaped, with some crossing to neighbouring Turkey or Turkish-held territory in Syria's north, according to the Britain-based Syrian Observatory for Human Rights war monitor.