So-called Islamic State figurehead Abu Bakr al-Baghdadi is believed to have been killed in a Russian airstrike.
Moscow's Defence Ministry reported al-Baghdadi died during a strike alongside other senior militants just outside the group's de facto capital in Syria.
Russia made the claim about the strike, carried out late last month, on Friday.
If confirmed, the death would mark a major military success for Russia, which has conducted a campaign in support of Syrian president Bashar Assad since September 2015.
Around 30 mid-level IS leaders were reportedly attending a meeting on the outskirts of Raqqa when they were targeted.
Three hundred other fighters were also killed in the drop.
The Russian Defence Ministry said the leaders had been discussing IS's withdrawal from Raqqa.
Drones were sent to monitor the area before Russian bombers and jets were dispatched to hit the gathering.
"According to the information that is being verified through various channels, IS leader Abu Bakr al-Baghdadi also attended the meeting and was killed in the airstrike," the ministry said in a statement.
It added that the US had been warned of the incoming strike.