The Islamic State jihadist group confirmed the death of its leader Abu Bakr al-Baghdadi in a statement Thursday and named his replacement as Abu Ibrahim al-Hashimi al-Quraishi.
"We mourn you... commander of the faithful," said Abu Hamza al-Quraishi -- presented as the jihadist group's new spokesman -- in an audio statement.
Baghdadi, who led ISIS since 2014 and was the world's most wanted man, was killed in a U.S. special forces raid in Syria's northwestern province of Idlib on Sunday.
The group also confirmed the killing in another raid the following day of the group's previous spokesman Abu Hassan al-Muhajir.
The statement said the jihadist group's legislative and consultative body convened after the 48-year-old Iraqi-born jihadist chief's death.
"The Islamic State shura council convened immediately after confirming the martyrdom of Sheikh Abu Bakr al-Baghdadi, and the elders of the holy warriors agreed" on a replacement, said the seven-minute message.
Little is known about Hashimi, whose name was seldom mentioned as a possible successor the multiple times that Baghdadi was reported killed in recent years.
"We don't know much about him except that he is the leading judge of ISIS and he heads the Sharia (Islamic law) committee," said Hisham al-Hashemi, an Iraqi expert on ISIS.
The ISIS spokesman also issued a stark warning to the United States, whose President Donald Trump announced Baghdadi's death in a televised address from the White House.
'Crazy old man'
"He died after running into a dead-end tunnel, whimpering and crying and screaming all the way," Trump said on Sunday, adding that Baghdadi "died like a dog".
In the new audio message, the new ISIS spokesman described Trump as "a crazy old man" and warned the U.S. that the group's supporters would avenge Baghdadi's death.
Abu Bakr al-Baghdadi Destroyed by U.S. Special Operators
"Do not rejoice America," he warned, "the new chosen one will make you forget the horror you have beholden... and make the achievements of the Baghdadi days taste sweet".
The spokesman also referred to an earlier call by Baghdadi for the thousands of ISIS fighters held in Syrian and Iraqi prisons to be freed.
Syrian Kurdish forces run prisons in northeastern Syria where they say around 12,000 ISIS suspects are held.
Most of those prisoners are Iraqi and Syrian but the detainees also include more than 2,000 foreigners who hail from more than 50 different countries.
With aerial and logistical assistance from an international coalition led by the US, Iraqi and Syrian forces have wrested back all the territory lost to ISIS in 2014.
Fighters from the newly-formed ISIS group that year swept through much of the Sunni heartland in Iraq and Syria to declare a "caliphate" that further expanded to reach roughly the size of Great Britain.
Years of battles led to the elimination in 2019 of ISIS' self-declared territorial "caliphate", ending an unprecedented experiment in jihadist statehood which saw a well-organised administration mint its own currency, produce school textbooks and levy taxes.
But while that entity collapsed in March in the remote eastern Syrian village of Baghouz, the organisation went underground and reverted to well-honed guerrilla tactics that continue to do damage.
A recent Turkish invasion targeting the Kurdish forces that had fought against ISIS in Baghouz has wrought havoc in northeastern Syria, whose geopolitical map is being redrawn.
Observers have warned that the power vacuum and confusion may create an opportunity for IS to rebuild and make fresh territorial gains.
ISIS has a very horizontal structure, analysts say, and the impact of a decapitation strike may be more symbolic than operational, leaving the group's global jihadist brand and efficiency as an insurgency largely intact.