The head of Russia's Security Council says there could be as many as 50,000 insurgents fighting for the Islamic State (IS) militant group in Syria and Iraq.
Nikolai Patrushev said at a meeting of the Security Council chiefs of the Commonwealth of Independent States (CIS) in Moscow that the IS was "getting stronger," and had between 30,000 and 50,000 fighters.
Western estimates have put IS forces at around 30,000 fighters, with some 3,000 coming from Western Europe.
Patrushev warned that many citizens of CIS countries have joined IS and their return to their home countries "is a serious challenge to the peace [and]...regional and national stability" of the CIS.
He added that IS fighters receive "good combat training."
The CIS Security Council heads are meeting ahead of the October 10 CIS summit in Minsk.