Moscow on Monday said it was struggling to confirm if the leader of the Islamic State group Abu Bakr al-Baghdadi is dead or alive, a month after reporting his possible demise.
The Russian army said in June that it was trying to verify information that its jets killed Baghdadi during a bombing raid near the IS stronghold of Raqa in Syria.
But over a month after the announcement Kremlin spokesman Dmitry Peskov said Russia still had "no more precise information" on Baghdadi's fate.
"The information coming in is contradictory and is being checked by the relevant agencies," he said.
Baghdadi, the undisputed leader of global jihadism, has been rumoured wounded or killed a number of times in the past.
The Britain-based Syrian Observatory for Human Rights, a monitor, said last week it had heard from senior IS leaders in Syria's Deir Ezzor province that Baghdadi was dead.
But Pentagon chief James Mattis said on Friday that he could not "confirm or deny" if Baghdadi is dead, adding that Washington's approach was to "assume he's alive until it's proven otherwise".
Baghdadi's group has earned global notoriety for imposing a hardline form of Islam that has included stonings, beheadings and amputations as it has claimed the creation of a "caliphate" after snatching territory across Syria and Iraq.
The fortunes of its "caliphate" have since turned with massive offensives launched by US-backed forces in Iraq and Syria.
Russia has been flying a bombing campaign in Syria since 2015 in support of its ally President Bashar al-Assad.