President Donald Trump will make a "major statement" at the White House at 9am on Sunday (US time), amid rumours Isis leader Abu Bakr al-Baghdadi has been killed by US-led forces.
Al-Baghdadi, the elusive militant who has been the subject of an international manhunt, has been in hiding for five years.
He has reportedly been killed in Idlib, Syria, after a raid, according to a senior US defence official. The CIA assisted in locating the Isis leader, CNN reported.
Baghdadi became the leader of Islamic State of Iraq (ISI) in 2010. In 2013, ISI declared its absorption of an al Qaeda-backed militant group in Syria and Baghdadi said that his group will now be known as Islamic State in Iraq and the Levant (ISIL or ISIS).
Trump gave an indication that something was afoot earlier on Saturday night when he tweeted without explanation, "Something very big has just happened!"
An administration official told CNN that the announcement is foreign policy related.
The Pentagon did not immediately respond to a request for comment.
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Newsweek, citing a US Army official briefed on the result of the operation, said al-Baghdadi had been killed in the raid.
Newsweek reported the president the mission nearly a week before it took place.
Early reports suggests Baghdadi may have detonated his suicide vest in the raid, killing himself.
Trump was expected to make the statement in the White House Diplomatic Reception Room, which he has used to make a number of major announcements.
Just last week he used the same room to announce that a ceasefire between Turkey and the Kurds had taken hold.
The strike came amid concerns that a recent American pullback from northeastern Syria could infuse new strength into the militant group, which had lost vast stretches of territory it had once controlled.
Al-Baghdadi cultivated Isis' reputation for beheadings and attracted hundreds of thousands of followers to a sprawling and self-styled caliphate in Iraq and Syria. He remained among the few Isis commanders still at large despite multiple claims in recent years about his death and even as his so-called caliphate dramatically shrank, with many supporters who joined the cause either imprisoned or jailed.
His exhortations were instrumental in inspiring terrorist attacks in the heart of Europe and in the United States. Shifting away from the airline hijackings and other mass-casualty attacks that came to define al-Qaida, al-Baghdadi and other IS leaders supported smaller-scale acts of violence that would be harder for law enforcement to prepare for and prevent.
They encouraged jihadists who could not travel to the caliphate to kill where they were, with whatever weapon they had at their disposal. In the US, multiple extremists have pledged their allegiance to al-Baghdadi on social media, including a woman who along with her husband committed a 2015 massacre at a holiday party in San Bernardino, California.
With a $25 million US bounty on his head, al-Baghdadi had been far less visible in recent years, releasing only sporadic audio recordings, including one just last month in which he called on members of the extremist group to do all they could to free Isis detainees and women held in jails and camps.
The purported audio was his first public statement since last April, when he appeared in a video for the first time in five years.
In 2014, he was a black-robed figure delivering a sermon from the pulpit of Mosul's Great Mosque of al-Nuri, his only known public appearance. He urged Muslims around the world to swear allegiance to the caliphate and obey him as its leader.
"It is a burden to accept this responsibility to be in charge of you," he said in the video. "I am not better than you or more virtuous than you. If you see me on the right path, help me. If you see me on the wrong path, advise me and halt me. And obey me as far as I obey God."
Though at minimum a symbolic victory for Western counterterrorism efforts, his death would have unknown practical impact on possible future attacks. He had been largely regarded as a symbolic figurehead of the global terror network, and was described as "irrelevant for a long time" by a coalition spokesman in 2017.
Al-Baghdadi was born Ibrahim Awwad Ibrahim Ali al-Badri al-Samarrai in 1971 in Samarra, Iraq, and adopted his nom de guerre early on. Because of anti-US militant activity, he was detained by US forces in Iraq and sent to Bucca prison in February 2004, according to Isis-affiliated websites.
He was released 10 months later, after which he joined the al-Qaida branch in Iraq of Abu Musab al-Zarqawi. He later assumed control of the group, known at the time as the Islamic State of Iraq.
After Syria's civil war erupted in 2011, al-Baghdadi set about pursuing a plan for a medieval Islamic State, or caliphate. He merged a group known as the Nusra Front, which initially welcomed moderate Sunni rebels who were part of the uprising against Syrian President Bashar Assad, with a new one known as the Islamic State of Iraq and the Levant.
Al-Qaeda's central leadership refused to accept the takeover and broke with al-Baghdadi.
Al-Baghdadi's fighters captured a contiguous stretch of territory across Iraq and Syria, including key cities, and in June 2014, it announced its own state — or caliphate. Al-Baghdadi became the declared caliph of the newly renamed Islamic State group. Under his leadership, the group became known for macabre massacres and beheadings —often posted online on militant websites — and a strict adherence to an extreme interpretation of Islamic law.
Over the years, he has been reported multiple times to have been killed, but none has been confirmed. In 2017, Russian officials said there was a "high probability" he had been killed in a Russian airstrike on the outskirts of Raqqa, but US officials later said they believed he was still alive.
- additional reporting wires