"There were two adult males taken off the objective, alive," Chairman of the Joint Chiefs of Staff Mark Milley said during a briefing at the Pentagon.

"They're in our custody and they're in a secure facility," Milley added, although he declined to provide more detail on the identity of the captives or how they were connected to Baghdadi.

US special forces conducted a weekend night time raid in northern Syria that led to the death of Baghdadi, who led the Islamic State extremist group, and killed a significant number of his fighters.

"While clearing the objective, US forces discovered al-Baghdadi hiding in a tunnel. The assault forces closed in on al-Baghdadi and ended when he detonated a suicide vest," said Milley.

The jihadist's remains were then transported to a secure facility to confirm his identity with forensic DNA testing, Milley said.

"The disposal of his remains has been done, is complete and was handled appropriately," he added.

Baghdadi was reportedly buried at sea, as was top Al-Qaeda terrorist Osama bin Laden after he was killed by US forces in a similar helicopter raid in Pakistan in 2011. Milley would not confirm the reports.

Milley also could not confirm the president's description of Baghdadi as "whimpering and crying" in his final moments.

The officer told reporters he didn't know who Trump's source was for the claim but suspected he had talked "directly to the unit members."

Milley confirmed however some video imagery of the operation would be publicly released after it goes through a declassification process.

While Baghdadi's death has deprived IS of its "inspirational leader," the security situation in Syria "remains complex," Defense Secretary Mark Esper told the briefing.

He added that US troops were in position to retain control of key oil fields in northeast Syria.

American forces will remain positioned in the strategic area "to deny ISIS access to those vital resources," and "overwhelming military force" will be used against any group that threatens their safety, Esper added.

Baghdadi's death will not rid the world of terrorism or end Syria's ongoing conflict, but it sends "a message to those who would question America's resolve," he said.

"The United States, more than any other nation in the world, possesses the power, and the will, to hunt to the ends of the Earth those who wish to bring harm upon the American people."