Russian defense ministry spokesman Igor Konashenkov announced on Tuesday that a battery of Russian S-300 air defense missile launchers has been transported to the Syrian city of Tartus to defend a Russian naval base and warships.

“The S-300 anti-aircraft missile system has indeed been sent to the Syrian Arab Republic,” Konashenkov said in a statement. “I remind you that the S-300 is a purely defensive system and poses no threat to anyone.”

“It’s not clear why the placement of S-300 in Syria has caused such a stir among our western colleagues,” he added.

The S-300 is a long-distance surface-to-air missile system and, with a range of up to 150 miles, is regarded as one of the most potent anti-aircraft missile systems currently fielded. The deployment of this system comes at a time that the United States suspended ceasefire talks.

Russia and America are at odds in Syria, with the Russian military supporting the regime of Syrian President Bashar Assad, and the US led coalition supporting rebels who oppose him. Syria has been embroiled in a civil war for over five years that has claimed the lives of over 300,000 people.