The angry statement comes amid signs of a Russian military build-up in Syria that has raised U.S. Concerns. Russian Deputy Foreign Minister Mikhail Bogdanov alleged that Bulgaria and Greece are facing pressure from Washington.
Bulgaria's Foreign Ministry earlier said the country is refusing to allow Russian military transport aircraft to fly through its airspace en route to Syria from September 1-24.
It said without elaboration that the reason for the refusal was "incorrect information" about the purpose of the flights and the cargo.
"If they make some restrictive or banning measures at American request, that raises a question about their sovereign right to make decisions about foreign planes crossing its airspace," Bogdanov said, according to the Interfax news agency. "If our Greek and Bulgarian partners have any doubts, they must explain what's the problem."
US defence officials, who spoke on condition of anonymity because they were not authorized to publicly discuss the sensitive issue, said the U.S. Has seen an increasing number of Russian transport planes seeking diplomatic approval for flights into Syria.
