The Russian navy has maintained a permanent detachment of about 10 warships in the Mediterranean Sea since late 2012, a top Russian Black Sea Fleet official said Thursday. Russia’s expanded military activity, both at home and abroad, has been a source of continued tension with Western leaders in recent months.

Russia’s three main naval fleets have each contributed ships to the standing Mediterranean force since it was first deployed, but the Black Sea Fleet commands the vessels, Russian Adm. Alexander Vitko told Russian agency Sputnik International News. It’s unclear which types of military vessels compose the permanent presence.

“Since the end of 2012, an average of 10 ships and auxiliary vessels from the Black Sea, Baltic and Northern fleets are permanently in the Mediterranean Sea, but the command of the permanently deployed navy in this region is carried by the Black Sea fleet and the burden of performing the tasks of this group lies namely on this fleet’s warships and auxiliary vessels,” said Vitko, the Russian Black Sea Fleet’s commander.

Confirmation of Russia’s permanent naval force in the Mediterranean was the latest example of Moscow’s ongoing bid to expand its military presence around the world. The Kremlin announced plans to spend trillions of rubles on upgrades to Russia’s armed forces by the end of 2020. Recently, Russia has expanded its long-range bomber patrols to reach as far as the Gulf of Mexico and conducted training exercises in regions as remote as the Arctic.

Officials in the United States and NATO have expressed growing concern with Russia’s military activity, particularly in Eastern Europe. Western leaders enacted economic sanctions against Moscow over its apparent involvement in the Eastern Ukraine conflict, with penalties to remain in place until European Union and U.S. diplomats were satisfied with Russia’s commitment to the peace process.

Earlier this year, Russia’s Black Sea Fleet conducted joint exercises with the Chinese navy in the Aegean Sea, a body of water to which the Mediterranean Sea directly connects. A Russian guided missile carrer participated in the drills, the Russian government-backed news agency Tass reported.