Russia has sent warships to the Mediterranean Sea in case it has to evacuate its citizens from Syria, Interfax news agency quoted a naval source as saying on Tuesday.

In what appeared the clearest sign so far that Russia is making firm preparations for a possible evacuation, a group of five ships, including two assault ships, a tanker and an escort vessel, left a Baltic Sea port on Monday, the source said.

The vessels were heading to the Mediterranean and could stay there for an indefinite period, Interfax said.

"They are heading to the Syrian coast to assist in a possible evacuation of Russian citizens ... Preparations for the deployment were carried out in a hurry and were heavily classified," it quoted the source as saying.

The report could not immediately be confirmed independently.

Interfax published its report after the Russian Foreign Ministry confirmed that two Russian citizens working in Syria had been kidnapped along with an Italian citizen.

The source said that anyone evacuated from Syria would be taken to Black Sea ports.

Deputy Foreign Minister Mikhail Bogdanov said last week that it was possible that President Bashar al-Assad's opponents might win the civil war in Syria and that Russia was looking at preparations for a possible evacuation.

Moscow is Syria's biggest arms supplier and has remained an ally of Assad throughout the 21-month-old uprising and has protected him from three consecutive U.N. Security Council resolutions meant to put pressure on him.

Russia has offices in Syria for state weapons exporter Rosoboronexport and maintains a small naval repair and maintenance base on the country's Mediterranean coast. – Reuters