No details have been released but Donald Trump expected to make statement at 9am Washington time
The US has carried out a raid in Syria targeting the Islamic State leader Abu Bakr al-Baghdadi, according to multiple reports.
A US official told Reuters an operation had taken place targeting the terrorist leader but did not say whether it had succeeded it capturing or killing him.
Newsweek said it had been told by a US Army official briefed on the raid that Baghdadi, 48, was dead. It said the operation took place in Syrias north-western Idlib province, and was carried out by special operations forces after receiving actionable intelligence.
Citing two senior administration officials, the New York Times reported that US special operations commandos had carried out a risky raid in north-western Syria on Saturday against a senior terrorist leader there, but did not name the person targeted.
Iran was informed by Syrian sources that Baghdadi had been killed, two Iranian officials told Reuters on Sunday.
Iran was informed about Baghdadis death by Syrian officials who got it from the field, one of the officials said.
Reuters was also told by Iraqi security sources that Baghdadi had been killed.
Our sources from inside Syria have confirmed to the Iraqi intelligence team tasked with pursuing Baghdadi that he has been killed alongside his personal bodyguard in Idlib, after his hiding place was discovered when he tried to get his family out of Idlib towards the Turkish border, one of the sources told Reuters.
The Syrian Observatory for Human Rights, a Syria war monitor, meanwhile reported that a squadron of eight helicopters accompanied by a warplane belonging to the international coalition attacked positions of the Hurras al-Deen (an al-Qaida affiliated group) where IS operatives were believed to be hiding in the Barisha area north of Idlib city.
Associated Press reported the observatory as saying nine people had died in the attack, but it was not known whether Baghdadi was one of them.
Earlier on Saturday the White House spokesman, Hogan Gidley, said Donald Trump planned to make a major statement at 9am on Sunday morning (1300GMT).
Gidley gave no further details, and it was unclear what the topic of the presidents statement might be.
The New York Times reported that the US defence secretary would appear on the morning shows to discuss developments in Syria, however it also reported that some analysts had expressed skepticism that Baghdadi would be hiding in Idlib.
The region is held by Hayat Tahrir al-Sham, an Islamist group that opposes Isis and routinely executes people thought to be affiliated with the group.
There was speculation, however, that Trump might have news about al-Baghdadi, who has been the subject of an international manhunt for years.
The president gave an indication that something was afoot earlier on Saturday night when he tweeted without explanation: Something very big has just happened!
Trump has faced withering criticism from Republicans and Democrats alike for his troop withdrawal from north-eastern Syria, which permitted Turkey to attack the USs Kurdish allies.
Many critics of Trumps Syria pullout have expressed worries that it would allow the Islamic State group to regain strength and pose a threat to US interests. An announcement about Baghdadis death could help blunt those concerns.
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. Last week he used the same room to announce that a ceasefire between Turkey and the Kurds had taken hold.
For days, US officials had feared that Isis would seek to capitalise on the upheaval in Syria. But they also saw a potential opportunity, in which Isis leaders might break from more secretive routines to communicate with operatives, potentially creating a chance for the US and its allies to detect them.
Baghdadi, who has $25m bounty on his head,was long thought to hiding somewhere along the Iraq-Syria border. He has led the group since 2010, when it was still an underground al-Qaida offshoot in Iraq.
On 16 September, Isiss media network issued a 30-minute audio message purporting to come from Baghdadi, in which he said operations were taking place daily and called on supporters to free women jailed in camps in Iraq and Syria over their alleged links to his group.
In the audio message, Baghdadi also said the US and its proxies had been defeated in Iraq and Afghanistan, and that the US had been dragged into Mali and Niger.
At the height of its power Isis ruled millions of people in territory running from northern Syria through towns and villages along the Tigris and Euphrates valleys to the outskirts of the Iraqi capital, Baghdad.
But in 2017, the fall of Mosul and Raqqa, its strongholds in Iraq and Syria respectively, stripped Baghdadi, an Iraqi, of the trappings of a caliph and turned him into a fugitive thought to be moving along the desert border between Iraq and Syria.
US air strikes killed most of his top lieutenants, and before Isis published a video message of Baghdadi in April there had been conflicting reports over whether he was alive.
Despite losing its last significant territory, Isis is believed to have sleeper cells around the world, and some fighters operate from the shadows in Syrias desert and Iraqs cities.
The group claimed responsibility for a series of suicide bombings in churches and hotels in Sri Lanka that killed more than 250 people in April, though police in the Indian Ocean island country say they are yet to establish a direct link to the terrorist group.