Russian news agencies are reporting that Moscow is sending three large landing ships with marines aboard to a Russian naval facility in the Syrian port of Tartus.
Three agencies quoted a source in the General Staff as saying the vessels, which are already in the Mediterranean, would arrive in Tartus this week or early next week.
They would be joined later by three other vessels from the Russian Navy's Black Sea and Northern Sea fleets.
Each ship would reportedly have up to 120 marines on board.
Russia is an ally of President Bashar al-Assad. Syria bought $US1 billion worth of weapons from Russia last year, about 8% of total Russian arms exports.
The goal of the mission was not specified, but Russia earlier said it was preparing to send marines to Syria in case it needed to protect personnel and remove equipment from the base.
Separately, a Syrian official said in Moscow that Damascus has reached an agreement to send crude oil to Russia in return for shipments of refined oil products.
Economic affairs deputy minister Qadri Jamil said it would be a barter deal. Syria has also asked for credit from Russia. The size and terms were yet to be decided.
Mr Jamil said Syria was producing about 200,000 barrels per day.