The White House is casting doubt on Russia’s claim that its forces killed Islamic State leader Abu Bakr al-Baghdadi in a late May airstrike in Syria.

A senior administration official says Russia would have “various different motives” for making such a claim, and the U.S. is not prepared to risk its credibility by corroborating the statement without independent evidence.

The official also noted that Russia’s claim that the strike killed more than 300 ISIS fighters is raising eyebrows in the national security community.

“That’s the type of magnitude that we would think we would’ve already seen reflections of,” the senior administration official said today.

Unsubstantiated reports of al-Baghdadi’s death have been frequent in recent years.