The Russian Defense Ministry is trying to verify whether ISIS leader Abu Bakr al-Baghdadi was killed in a strike in late May along with other senior group commanders.
In a statement, Russia claims the airstrike was carried out during a meeting of ISIS leaders outside the group's de facto capital of Raqaa in Syria.
The report of al-Baghdadi's death comes as ISIS has suffered major setbacks.
U.S. and coalition forces have been increasing the pressure in their battle against ISIS in Syria.
Secretary of Defense James Mattis told CBS News that his order from President Donald Trump is to eliminate the Islamic terror group once and for all.
"We have already shifted from attrition tactics where we shove them from one position to another in Iraq and Syria to annihilation tactics where we surround them," said Mattis.
Meanwhile, a spokesman for the U.S.-led anti-Islamic State coalition said he could not confirm reports that al-Baghdadi had been killed.
And in an email statement, U.S. Army Col. Ryan Dillon said, "We cannot confirm these reports at this time."
U.S. authorities had offered a $25 million reward for information leading to al-Baghdadi's capture.