United States officials have said the body of militant Islamic State group 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.

Syrian Kurds claimed to be a key source of the intelligence that led Americans to Baghdadi after years of tracking the man behind a five-year reign of terror across much of Iraq and Syria.

And an unnamed US military dog became an unlikely hero of the raid, incurring injuries as it chased Baghdadi down a dead-end tunnel underneath his northwestern Syria hideout, where the militant blew himself and three children up with a suicide vest.

Read: Abu Bakr al-Baghdadi, the low-profile boss of militancy world in Middle East

The US military basked in success on Monday after eliminating the founder and spiritual guide of the IS group, capping a years-long campaign to crush the extremist organisation that had at one point created a “caliphate” the size of England.

"His death marks a devastating blow to the remnants of [IS]," said Defense Secretary Mark Esper.

Raid undertaken 'brilliantly'

He praised the nearly hundred-strong force that helicoptered to the rural compound in the Idlib region of Syria in a complex mission that required coordination with Russians, Kurds, Turks and President Bashar al-Assad's regime to prevent US aircraft from being fired upon.

"They executed the raid in all of its facets brilliantly," Esper said.

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 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 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.

Baghdadi's underwear

A Kurdish official said an inside source the group oversaw was responsible for leading US forces to Baghdadi's hideout, helping to map out the interior of the compound, its staffing, as well as making it possible for them to identify the IS chief.

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

The group had an informant who was able to infiltrate Baghdadi's house.

"Al-Baghdadi changed his places of residence very often," he said on Twitter.

"Our intelligence source was involved in sending co-ordinates, directing the airdrop, participating in and making the operation a success until the last minute," Polat Can said.

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

'Beautiful' military dog

Attention focused as well on the unnamed dog — likely a Belgian Malinois, a breed favoured by the military, which chased Baghdadi into a tunnel under the complex and cornered him before he detonated his suicide vest.

Trump praised the dog on Sunday as "beautiful", but military officials said any information about it, including its name, was secret.

"It's classified, we're protecting the dog's identity," said Milley.

The dog had been "slightly wounded and is fully recovering", he said.

US will not police Syria

On Monday, Saudi Crown Prince Mohammad bin Salman offered US President Donald Trump his congratulations on the raid.

"The Crown Prince congratulated the President on the United States successful mission to bring ISIS founder and leader Abu Bakr al-Baghdadi to justice," the White House said in a statement.

US officials said Baghdadi's death would not end the conflict in Syria, but warned Washington could not be relied on to bring peace to the region.

"Baghdadi's death will not rid the world of terrorism or end the ongoing conflict in Syria," said Esper.

"The security situation in Syria remains complex," he said, adding: "Acting as a police force out to solve every dispute is not our mission."

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