BEIRUT • The United States' declaration of Abu Bakr al-Baghdadi's death opens the question of his succession at the helm of ISIS, and analysts say the list looks short.
It was limited further on Sunday night after Kurdish fighters in Syria said they had killed ISIS spokesman Abu Hassan al-Muhajir - another prominent figure - in a joint operation with US forces.
ISIS social media channels have neither confirmed US President Donald Trump's announcement on Sunday that Baghdadi had been killed in a US raid in Syria, nor alluded to potential successors.
But Mr Hisham al-Hashemi, an Iraqi expert on the Islamic State in Iraq and Syria, said two potential candidates stand out: Abu Othman al-Tunsi and Abu Saleh al-Juzrawi, who is also known as Hajj Abdullah.
The first - a Tunisian national - heads ISIS' Shura Council, a legislative and consultative body, Mr Hashemi said.
The second - a Saudi - runs the militant group's so-called Delegated Committee, an executive body, he added.
These "possible options" would nonetheless be controversial, according to the ISIS expert, because they are not Syrian or Iraqi nationals, who make up the bulk of ISIS' guerilla force. "This could lead to defections," he said.
Mr Aymenn Jawad Tamimi, an academic and expert on radical Islamists, also identified the elusive Hajj Abdullah as a potential successor.
"He turns up in leaked IS documents as a deputy of Baghdadi and to my knowledge, he is not dead," Mr Tamimi said, using another name of ISIS. "Apart from some texts that mention Hajj Abdullah, not much is known about him except that he was the emir of the Delegated Committee, which is the general governing body of IS."
Speculation has abounded around a senior ISIS figure known as Abdullah Qardash - a former Iraqi military officer jailed with Baghdadi in the US-run Iraqi prison of Camp Bucca.
A months-old statement attributed to ISIS propaganda arm Amaq but never officially adopted by the group said he was selected to replace Baghdadi even before Mr Trump declared the self-proclaimed "caliph" dead.
But Mr Tamimi and Mr Hashemi both said the statement was fake.
Citing Iraqi intelligence sources, Mr Hashemi said Qardash had died two years ago. Mr Hashemi also said Qardash - a Turkmen from Iraq's Tal Afar region - would not qualify as "caliph" because he is not from the Quraysh tribe - the same tribe as Prophet Muhammad.
He said belonging to the Quraysh tribe is seen as a prerequisite for becoming the leader of ISIS.
Whoever gets the job will inherit the difficult task of leading a frayed organisation that has been reduced to scattered sleeper cells after continuous offensives stripped it of its territory in Iraq and Syria.
Divisions have widened within ISIS ranks in recent months, with some supporters blaming Baghdadi for the demise of the "caliphate" in March.
ISIS has invested in an elaborate bureaucratic structure that could compensate for the loss of its leader, according to Mr Charlie Winter, a researcher at King's College London.
"(Militant) groups are most likely to survive or strengthen through decapitation strikes when they have bureaucratic systems and structures in place," he told news agency Agence France-Presse. "Few (if any) have as many bureaucratic systems and structures as IS, so I'd expect it to double down, not disintegrate."