The deputy director of the agency that supervises Russia's arms trade has been quoted as saying Russia will not deliver fighter planes or other new weapons to Syria while the situation there remains unresolved.
Interfax news agency reported Vyacheslav Dzirkaln of the Federal Service for Military Technical Co-operation as saying:
"While the situation in Syria is unstable, there will be no new deliveries of arms there.''
He was speaking at the Farnborough Airshow in Britain.
If confirmed, this could signal the strongest move yet by Moscow to distance itself from the regime of President Bashar al-Assad, which up to now it has defended from harsher sanctions.
It could also scuttle up to $US4 billion of outstanding contracts, including fighter jets and air defence systems which were expected to be delivered this year.
Mr Dzirkaln was also quoted as saying Russia would not deliver a shipment of 36 Yak-130 fighter planes.
"In the current situation talking about deliveries of airplanes to Syria is premature," he said.
Rosoboronexport would not comment on the remarks, which were also reported by the RIA news agency.
Syria's arms trade ties with Moscow date back to the Soviet era.
