Russia’s decision to send S-300 missile systems to Syria is, in part, a message to the United States, according to the head of the Russian parliament’s Foreign Affairs Committee, Alexei Pushkov.

Russia opposes outside interference in Syria’s ongoing civil war, he explained, according to Walla. “We’re opposed to no-fly zones, because they are the first step toward aerial attack,” he said.

“Syria asked Russia to help it defend itself from aerial assault,” he added.

In early May at least two Syrian military targets were hit in what Syria has said were Israeli airstrikes.

According to the Wall Street Journal Russia has sent at least 12 warships to patrol near a Russian Navy base in Syria. According to the report, American and European leaders have widely interpreted the move as a warning to the West and to Israel not to interfere in Syria.

The reported deployment is one of the Russian Navy’s largest since the end of the Cold War.

Russian Foreign Minister Sergei Lavrov has stated that Russia agreed to the S-300 sale based on previous agreements. Russia does not intend to sell Syria new weapons, he said, but will fulfill old commitments.

“We do not want our reputation as reliable suppliers of weapons to be affected,” he said.