Amid reports of a Russian military build-up in Syria, Washington has warned the Kremlin against escalating the conflict. Fears are rising that Moscow could be preparing a combative backing of the Assad regime.
US Secretary of State John Kerry warned his Russian counterpart over unconfirmed reports of Moscow's plans to directly intervene in the Syrian conflict, in a phone call on Saturday.
Kerry told Foreign Minister Sergey Lavrov that if a report in "The New York Times" on Saturday was accurate, Russia's actions could further intensify the four-year-old conflict, according to a statement by the US State Department.
Russia's involvement could "lead to greater loss of innocent life, increase refugee flows and risk confrontation with the anti-'Islamic State' (IS) coalition operating in Syria," it added.
According to "The New York Times," Russia has delivered a portable air traffic control system and prefabricated housing units for hundreds of people at a Syrian airfield. Citing unnamed administration officials, the paper said the Russians have filed military overflight requests across bordering countries throughout September.
Last week, Israeli media reported that Russia planned to send warplanes to Syria to fight the "Islamic State."
Raising the stakes
But on Friday, Russian President Vladimir Putin said it was premature to speak of deploying Russian soldiers against the jihadist group. He did confirm the provision of training and logistical support to the Syrian army.
Russia remains a close ally of Syrian President Bashar al-Assad and has been providing weapons and other military equipment to Damascus since Soviet times. Moscow also maintains a small naval facility at the Syrian port of Tartous on the Mediterranean Sea.
Moscow has used its United Nations veto to block several attempts by Western diplomats to oust Assad.
On Friday, Putin once again backed the Syrian leader, adding that Assad was ready to share power with a "healthy" opposition.