Laith Alkhouri, a director at Flashpoint, a business risk intelligence company in New York that tracks militant threats and cyberthreats, also expressed skepticism.

“At this time, I’m not seeing credible chatter to verify the claim by Russia,” he said. “Al-Baghdadi has been claimed killed multiple times before, and none of the previous claims proved legitimate.”

Russia’s foreign minister, Sergey V. Lavrov, himself introduced a note of caution when asked about the Russian military’s reports. “So far, I do not have 100 percent confirmation of this information,” he said at a news conference.

Mr. Lavrov also cautioned that the Islamic State was likely to survive the possible death of its leader. “Examples of such actions to destroy or ‘behead’ a terrorist group have always been presented with great enthusiasm,” he said. “However, history shows that the fighting capacity of these structures was restored.”

Russia intervened in the Syrian civil war in 2015; it said at first that cargo planes flying to a Syrian air base carried only humanitarian aid, but later openly announced a military operation. The Kremlin’s stated goal was fighting the Islamic State, lest it gain a stronghold in Syria not far from restive, predominantly Muslim regions in southern Russia.

But the Obama administration said that the pattern of airstrikes showed that Russia’s real intention was to prop up the government of President Bashar al-Assad, a Russian ally battling a range of opposition groups, including moderate rebels. The killing of the Islamic State’s leader, if confirmed, would help bolster Russia’s initial justification for its intervention — that its goal all along was to fight terrorism.

In its statement on Friday, the Russian Defense Ministry said that it had “warned the American side about the strike in advance,” but it was unclear whether Russia had shared intelligence on the meeting or cooperated in any other way with the Western-led coalition fighting in Syria. The United States and Russia do not typically share intelligence from their missions in Syria.