MOSCOW — A tiny, frayed Russian military base on Syria’s Mediterranean coast has jumped into international focus amid concern over how far Russia might go to bolster the government of President Bashar al-Assad.

The site, at the port of Tartus, is little more than a pier, fuel tanks and some barracks. But it is the last Russian military base outside the former Soviet Union, and its only Mediterranean fueling spot, sparing Russia’s warships the trip back to their Black Sea bases through straits in Turkey, a NATO member.

Russian officials have twice this year denied reports that they are reinforcing the garrison at Tartus with marines, most recently on Friday. On Monday, the news agency Interfax cited an unnamed officer identified as a member of the Navy General Staff as saying two landing craft — the Nikolai Filchenkov and Cesar Kunikov, based in Sevastopol — and an oceangoing tugboat were prepared for an extended mission to Syria. A spokesman for the Black Sea fleet, Capt. Vyachislav V. Trukhochyov, declined to confirm this, saying in a telephone interview from Sevastopol that both ships mentioned in the Interfax report were still moored at their docks. Still, the reports underscore the importance of the base as a Russian outpost, staffed by uniformed members of the Russian armed services on the coast between Western navies and the fighting inland. It is a tripwire that must be stepped over carefully by any Western nation that decides to intervene to halt the violence in Syria, an option being discussed more vigorously as diplomatic efforts fail.

Moscow has been a close ally of Syria since the 1973 Arab-Israeli war and has regularly supplied its military in conflicts since. Along with its modest garrison at Tartus, Russia has military officers in Syria under the auspices of its embassy and civilian technical advisers working irregularly on Russian-made air defense systems and repairing airplanes and helicopters in Syria, all of which present obstacles to Western intervention.