France, Britain, and NATO say they are concerned about a "very significant" increase in Russia's military presence in Syria.
French Defense Minister Jean-Yves Le Drian called on Moscow to justify its "very significant" Russian buildup in Syria.
Le Drian said while meeting on September 24 in Paris with British Defense Secretary Michael Fallon that if Russia's main intention is "to protect [Syrian] President Bashar al-Assad," then it should say so.
Fallon said the Russian military buildup in Syria "will only complicate what's already a very complicated and difficult situation."
NATO Secretary-General Jens Stoltenberg said he too is "concerned" by Moscow's actions in Syria and said it is important for the Russians to make clear "what are their intentions."
The comments came as Russia announced it would conduct naval ,maneuvers in the eastern Mediterranean this month as well as in October.
The Russian Defense Ministry said on September 24 the exercises were planned last year and did not link them to the situation in Syria.
Russia has been one of Syria's strongest allies throughout the four-year civil war that has killed some 250,000 people.
Based on reporting by Reuters and AFP