The US declaration of Abu Bakr al-Baghdadi's death opens the question of his succession at the helm of the Islamic State jihadist organisation and analysts say the list looks short.
It was limited further on Sunday night after Kurdish fighters in Syria said they had killed IS spokesman Abu Hassan al-Muhajir -- another well-known figure -- in a joint operation with US forces.
IS social media channels have not confirmed President Donald Trump's announcement on Sunday that Baghdadi had been killed in a US raid in Syria, nor alluded to potential successors.
But Hisham al-Hashemi, an Iraqi expert on IS, 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 IS's Shura Council, a legislative and consultative body, Hashemi said.
The second -- a Saudi -- runs the jihadist group's so-called Delegated Committee, an executive body, he added.
These "possible options" would nonetheless be controversial, according to the IS expert, because neither is a Syrian or Iraqi national, who make up the bulk of IS's landless guerilla force.
"This could lead to defections," he said.
Aymenn Jawad Tamimi, an academic and expert on jihadists, 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," Tamimi said.
"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."
- Rumours -
Speculation has abounded around a senior IS figure known as Abdullah Qardash - a former Iraqi military officer jailed with Baghdadi in the giant US-run Iraqi prison of Camp Bucca.
A months-old statement attributed to IS propaganda arm Amaq but never officially adopted by the group said he was selected to replace Baghdadi even before Trump's declared the self-proclaimed "caliph" dead.
But Tamimi and Hashemi both said the statement was fake.
Citing Iraqi intelligence sources, Hashemi said that Qardash had been dead since 2017.
"Qardash's daughter is currently held by Iraqi intelligence," he said. "Both her and other relatives have confirmed that he died in 2017."
Hashemi also said that 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 the Prophet Mohammad.
He said belonging to the Quraysh tribe is seen as a prerequisite for becoming the leader of IS.
- Tricky succession -
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 IS ranks in recent months, with some supporters blaming Baghdadi for the demise of the "caliphate" in March and for being absent when it died.
With Baghdadi gone, "IS affiliates have a chance to switch allegiances or simply not re-pledge their allegiance to Baghdadi's successor," said Nate Rosenblatt, a researcher and jihad expert.
This may give a boost to rival jihadist groups in Syria such as Hayat Tahrir al-Sham, headed by Al-Qaeda's former Syria affiliate, and the Al-Qaeda-linked Hurras al-Deen group, he said.
Both have been trying to root out IS locally.
- 'It doesn't matter'-
But day-to-day IS operations are not likely to be impacted by the leadership void, according to Max Abrahms, professor of political science at Northeastern University.
"It doesn't matter who will succeed Baghdadi," who largely disappeared after he announced his "caliphate" across swaths of territory in Syria and Iraq in 2014, he said.
"When it comes to decision making and operations and recruitment, IS was much more decentralised than even Al-Qaeda," whose founder Osama bin Laden was also killed a US raid in 2011, he added.
"When Bin Laden was killed, the question of who would replace him was more relevant, because Bin Laden exercised more control over Al-Qaeda than Baghdadi did over IS."
IS has invested in an elaborate bureaucratic structure that could compensate for the loss of its leader, according to Charlie Winter, a researcher at King's College London.
"Jihadi groups are most likely to survive or strengthen through decapitation strikes when they have bureaucratic systems and structures in place," he told AFP.
"Few (if any) have as many bureaucratic systems and structures as IS, so I'd expect it to double down, not disintegrate."