Al-Baghdadi was believed to be in Mosul, Iraq, prior to a US -led coalition effort in October 2016 to take the city.
In October 2011, the U.S. officially designated Baghdadi as a "terrorist".
One of the best known IS commanders, Abu Mohammed al-Adnani, the spokesman who frequently released audio messages calling for stepped-up attacks, was also killed past year.
It is unclear how much of a role he has played in ISIS militarily or strategically, or how much impact his death would even have on the group, other than symbolically.
But a spokesman for the United States-led coalition against ISIS said he could not verify that al-Baghdadi had been killed.
He is not, however, known to have travelled to Raqqa in recent months, where Kurdish militias, backed by the U.S., have been edging towards a city that had been the group's Syrian stronghold since early 2013. It is believed the leader has been in hiding. But US officials stopped short of dismissing the report altogether, because it is hard to disprove such a claim.
The Defence Ministry added that it had warned the USA of the coming strike.
The Russians have made similar claims in the past, U.S. officials said.
Okay, so that announcement came from the Russian Defense Ministry.
According to media reports, al-Baghdadi was brought up in a religious family.
This file image made from video posted on a militant website Saturday, July 5, 2014, purports to show the leader of the Islamic State group, Abu Bakr al-Baghdadi, delivering a sermon at a mosque in Iraq during his first public appearance.
Hoshiyar Zebari, a long-serving former Iraqi foreign minister and now a senior adviser to the government of the Kurdish autonomous region, also told Reuters there was no confirmation of Baghdadi's death.
Russian Federation said Friday that it killed ISIS leader Abu Bakr al-Baghdadi and other leaders in a strike in late May, a claim US officials could not confirm.
None of the names given by the Russians, with the exception of al-Baghdadi's, is known by CBS News to belong to a senior figure in the ISIS group.
But in the absence of independent confirmation, some US officials said USA agencies were sceptical of the report.
Answering reporters' questions, the Kremlin spokesman refused to weigh the Russian airstrike on Raqqa's southern suburbs that had presumably killed the IS leader.
It was unclear whether the Russian military had targeted Baghdadi, or learned of his presence at the gathering after the strike.
This is the first time, however, that Russian Federation has said it may have killed the IS leader.
Under Baghdadi's leadership ISIS thugs have shocked the world with their sadistic and savage murder of thousands of people in the Middle East and Europe.
Baghdadi hasn't exactly been in the spotlight over the last few months.
In March, US secretary of state Rex Tillerson declared that Baghdadi's death was imminent as "nearly all" of his deputies were dead and "it is only a matter of time" before the ISIL chief himself met the same fate.