Greece has received a request from the United States to deny Russia the use of Greek airspace for aid flights to Syria, a spokesman for the foreign ministry in Athens said.

The spokesman said the request was being examined.

Russian newswire RIA Novosti earlier said Greece had refused the U.S. request, citing a diplomatic source, adding that Russia was seeking permission to run the flights up to Sept. 24.

Greece has sought to foster closer ties with Russia during the economic crisis that nearly forced it out of the euro zone.

The Russian foreign ministry was not immediately available for comment.

Russia is a long-time ally of Syrian President Bashar al-Assad, whose rule the United States and other western powers favour ending via a political transition.

The request from Washington comes after it expressed concerns to Moscow on Saturday about reports that Russia was moving toward a major military build-up in Syria widely seen as aimed at bolstering Assad.