Russia has claimed that Nato is preparing to impose a no-fly zone in Syria to protect rebel fighters, a move that would dramatically escalate the 10-month uprising.
Nikolai Patrushev, who heads the Kremlin's security council, said that he had received intelligence suggesting that the military alliance is planning a Libya-style intervention, a step that Moscow has repeatedly warned the international community against.
"We are getting information that Nato members and some Persian Gulf states intend... direct military intervention," the confidant of premier Vladimir Putin told Russia's Kommersant newspaper.
The claims, however, were immediately denied by Nato. Spokeswoman Carmen Romero told Bloomberg that there was, "no discussion of a Nato role with respect to Syria". A number of Nato members also denied Mr Patrushev's claims.
Russia, a major arms supplier to Syria, has emerged as one of the main stumbling blocks to Western efforts to curb President Bashar al-Assad's crackdown against the uprising.
Mr Patrushev said that any military action against Syria by Nato would most likely be led by Turkey, suggesting that Ankara was battling for hegemony with Iran, Syria's major backer.
"This time it is true that the main strike forces will not be provided by France, the UK or Italy, but possibly by neighbouring Turkey which was until recently on good terms with Syria and is a rival of Iran with immense ambitions," he said.