Three Russian warships crossed the Bosphorus on Thursday en route to the eastern Mediterranean amid rising concerns over a potential military intervention by the U.S. in Syria.
Moscow is a key ally of the Syrian regime and has kept a constant presence of four warships in the region.
Meanwhile Turkey has sent military tanks and armoured vehicles to the border with Syria to reinforce units already there.
In the town of Hatay, Turkish health authorities have set up field hospitals and makeshift chemical detoxification tents to prepare for the possible arrival of large numbers of refugees.
The military convoys arrived at the border province of Hatay as Turkish health authorities erected field hospitals and makeshift chemical detoxification tents to prepare for a potential refugee influx.
Turkey has said previously it would be ready to take part in any international action against Assad, even outside the auspices of the United Nations.