"The pressure being applied by the United States causes particular concern," Russian Defense Ministry official Oleg Dogayev was quoted as saying by Itar-Tass news agency on Tuesday.
He said "the dispatch of ships armed with cruise missiles toward Syria's shores has a negative effect on the situation in the region."
Five US destroyers and an amphibious ship are in the Mediterranean, poised for possible cruise missile strikes against Syria, and US officials said the aircraft carrier USS Nimitz and four other ships in its strike group moved into the Red Sea on Monday.
Russia opposes military intervention over an alleged chemical weapons attack in Syria. Moscow is also sending new warships to the Mediterranean but says it is just rotating ships in the area.
The call for military action against Syria intensified after foreign-backed opposition forces accused the Syrian government of launching a chemical attack on militant strongholds in the suburbs of Damascus on August 21.
Damascus has vehemently denied the accusations, saying the chemical attack was carried out by the militants themselves as a false flag operation.
Syria has been gripped by deadly unrest since 2011. According to reports, the Western powers and their regional allies -- especially Qatar, Saudi Arabia, and Turkey -- are supporting the militants operating inside Syria.
According to the United Nations, more than 100,000 people have been killed and a total of 7.8 million of others displaced due to the violence.