ISIL leader Abu Bakr al-Baghdadi appears for the first time in five years in a video released by his group in April 2019. It is unclear when the footage was filmed.Photo: VCG

US officials have said the body of Islamic State (IS) 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 jihadist blew himself and three children up with a suicide vest. 

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

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

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 Syrian 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 General 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. 

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 Baghdadi. 

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