Russia sent two corvettes, an oiler, and a tug boat to the Eastern Mediterranean off the coast of Syria days after two US Navy ships fired 59 cruise missiles at an airfield controlled by Syrian President Bashar al-Assad, a defense official told the US Naval Institute.

The ships should reach the area within the next several days.

Tensions between the US and Russia have peaked since the US struck Russia’s stalwart ally, Assad, over what the US believes was a chemical weapons attack orchestrated by Syrian and Russian forces.

Russia has warned of “extremely serious” consequences for the US strike and reportedly suspended key military agreements with the US that heighten the risk of war.