Islamic State confirmed on Thursday that its leader Abu Bakr al-Baghdadi was killed in a weekend raid by U.S. special forces in northwestern Syria, and vowed revenge against the United States.

The United States has given the remains of Islamic State leader Abu Bakr al-Baghdadi a burial at sea and afforded him religious rites according to Islamic custom after he was killed in a U.S. commando raid in Syria on Saturday, three officials told Reuters.

Islamic State's media network on Monday published a threatening video message purporting to come from its leader Abu Bakr al-Baghdadi in what would be his first appearance since declaring the jihadists' now-defunct "caliphate" five years ago.

The U.S.-led coalition told Reuters on Friday that it does not have "any releasable information concerning the whereabouts" of Islamic State leader Abu Bakr al-Baghdadi.

A Hezbollah-run media unit said on Friday Islamic State leader Abu Bakr al-Baghdadi was reported to have been in the Syrian town of Albu Kamal during the Syrian army and its allies’ operation to clear it.

If Islamic State leader Abu Bakr al-Baghdadi is confirmed dead, he is likely to be succeeded by one of his top two lieutenants, both of whom were Iraqi army officers under late dictator Saddam Hussein.

Moscow said on Friday its forces may have killed Islamic State leader Abu Bakr al-Baghdadi in an air strike in Syria last month, but Washington said it could not corroborate the death and Western and Iraqi officials were skeptical.

Islamic State leader Abu Bakr al-Baghdadi is on the brink of losing the two main centers of his 'caliphate' but even though he is on the run, it may take years to capture or kill him, officials and experts said.