Washington: The US State Department has accused Russia of having a "morally bankrupt" policy over Syria.
The US reaction came two days after Turkey intercepted a Syrian passenger jet headed from Moscow to Damascus over suspicions it had military equipment on board.
"No responsible country ought to be aiding and abetting the war machine of the Assad regime and particularly those with responsibilities for global peace and security as UN Security Council members have," State Department spokeswoman Victoria Nuland told reporters.
On Wednesday, Turkish fighter jets had forced the jet to land on its soil and seized what it said was ammunition and military gear bound for Syria.
Nuland said the US had "grave concern" that Russia is continuing to supply Syrian government forces with material that could be used against rebels struggling to topple President Bashar Assad`s regime.
On Friday, Russian Foreign Minister Sergei Lavrov said that the plane was legally carrying Russian radar parts for Syria. "We have no secrets," Lavrov told journalists in Moscow. "There were, of course, no weapons on board and there could not have been."
Lavrov also stressed the delivery was "entirely legal" and that Russia would demand both the return of the equipment and an explanation from Turkey.
US State Department spokeswoman Nuland said the shipment was "legally correct", but "the policy is still morally bankrupt".