US officials said the body of "Islamic State of Iraq and Syria" (ISIS) chief Abu Bakr al-Baghdadi was buried at sea, as fresh details surfaced about the US special forces operation that led to his death over the weekend.

The raid, named for Kayla Mueller, a US aid worker who was kidnapped and killed by ISIS, capped a years-long campaign to crush the extremist group and the man behind a five-year reign of terror across much of Iraq and Syria.

"His death marks a devastating blow to the remnants of (ISIS)," said US Defence Secretary Mark Esper.

He praised the nearly hundred-strong force that helicoptered to the compound in Idlib in a complex mission that required co-ordination with Russians, Kurds, Turks and the Syrian regime to prevent US aircraft from being fired upon.

Joint Chiefs of Staff Chairman Gen. Mark Milley said no one was injured in the operation, despite the US team taking fire when they arrived.

They took two men prisoner, and al-Baghdadi's body was taken to a secure facility for a DNA test that would confirm his identity, Milley said.

"The disposal of his remains has been done, is complete and was handled appropriately," he added, saying it was handled "in accordance with the law of armed conflict".

Another Pentagon official confirmed that al-Baghdadi's body was put into the sea at an unnamed location, similar to the 2011 sea burial of al-Qaeda leader Osama bin Laden after his death in a US special forces raid in Pakistan.

Al-Baghdadi's underwear

A Kurdish official said an informant was responsible for leading US forces to al-Baghdadi's hideout, helping to map out the interior of the compound, its staffing, as well as making it possible for them to identify al-Baghdadi.

"Since May 15th, we have been working together with the CIA to track al-Baghdadi and monitor him closely," said Polat Can, a senior adviser to the Syrian Democratic Forces (SDF).

The SDF had an informant who was able to infiltrate al-Baghdadi's house and "was involved in sending co-ordinates, directing the airdrop, participating in and making the operation a success until the last minute", Can said.

The source "brought al-Baghdadi's underwear to conduct a DNA test and make sure (100%) that the person in question was al-Baghdadi himself", he said.

"Al-Baghdadi's death will not rid the world of terrorism or end the ongoing conflict in Syria," Esper said, noting that "the security situation in Syria remains complex".

But he said the ISIS leader's death "will certainly send a message to those who would question America's resolve and provide a warning to terrorists who think they can hide".