Russia says two of its Buyan-class missile corvettes are heading back to join its forces stationed in the Mediterranean Sea as the conflict in Syria deepens following the US suspension of contacts with Moscow over the Syrian crisis.

Captain 2nd Rank Nikolai Voskresensky, a spokesman for Russia's Black Sea Fleet, told Russian news agencies on Wednesday that the Zelyony Dol and Serpukhov warships left their home port in Crimea on Tuesday as part of Moscow's rotational naval forces in the region.

The two small missile ships, which embarked on a long voyage from the Crimean port of Sevastopol on October 4, “have passed the Black Sea straits and will enter the Mediterranean waters in the evening,” Voskresensky said.

The vessels are set to join the Russian Navy's “permanent task force in the Mediterranean as part of a planned offshore maritime zone rotation," the official added.

The two ships are returning to the Mediterranean after carrying out missile strikes against militants' positions in Syria on August 19 as part of their earlier deployment off the coast of Syria.

The redeployment comes a day after Russia’s Defense Ministry spokesman, Igor Konashenkov, said that his country had dispatched the S-300 surface-to-air missile defense system to Syria in a bid to defend Russia’s naval base in the Syrian city of Tartus.

Earlier this week, Washington suspended its participation in bilateral channels with Moscow, which were established to maintain a ceasefire in Syria.

The announcement came two weeks after the latest US-Russia-brokered truce in Syria came to an end after Damascus’ refusal to extend the deal as a result of deadly US-led air raids on a Syrian military base near the eastern city of Dayr al-Zawr in violation of the agreement.

Since March 2011, Syria has been hit by militancy it blames on some Western states and their regional allies. Moscow and Washington support opposing sides in the crisis.

Russia has been conducting airstrikes against Daesh and other terrorist groups in Syria at the Damascus government’s request since September 2015.