Russia has sent a naval flotilla of seven warships led by an anti-submarine destroyer to its Syrian base at Tartus, according to Interfax news agency.
According to sources cited by Interfax, the ships were carrying marines on a training mission, as well as food and fuel for the maintenance and repair base.
BBC diplomatic correspondent Jonathan Marcus says that, by any standards, the flotilla is a significant naval deployment.
He says Moscow appears to be sending a signal to the Syrian regime that it is putting a force into the Mediterranean that could be used to extricate Russian personnel and equipment from their naval base, should it be required.
Equally Moscow is signalling to the US and the West that it intends to defend its interests in the region, our correspondent adds.
See this for background.
Syria is only 883 miles from Iran, and so all of this is being played out within a fairly small area.