Russia has said it has not made any new deliveries of military helicopters to Syria.
However, Moscow said it had sent repaired aircraft to the violence-torn country "many years ago".
It is the most direct response yet to US Secretary of State Hillary Clinton's comments that Washington had information attack helicopters were on the way from Russia to Syria.
The Foreign Ministry said Moscow's arms cooperation with Damascus was limited to "defensive" technology.
It said it is not sending Syria weapons that could be used in the internal conflict.
"There are no new deliveries of Russian military helicopters to Syria. All arms industry cooperation with Syria is limited to a transfer of defensive arms," the ministry said on its website.
"Regarding helicopters, there were previously planned repairs of military equipment delivered to Syria many years ago."
Moscow says it is fulfilling existing contracts for air defence systems supplies for use against external attacks.
Russia faces increasing Western criticism over arms supplies to Syria where the United Nations says government forces have killed more than 10,000 people in a crackdown on an uprising that began with pro-democracy protests in March 2011.
A source close to Russia's arms exporting monopoly Rosoboronexport said that Mrs Clinton's comments may have referred to helicopters that had been sent to Russia in 2009 for repairs and may be on the way back to Syria.
Christian target claims rejected
Meanwhile, the Vatican's ambassador to Syria has rejected reports that Christians there are being targeted by Opposition forces, insisting that they are sharing in the suffering of all citizens.
Fears have been expressed that the Christian minority will become more of a target as the fighting continues.
Some senior Christians have already addressed pro-Government rallies.
On Tuesday, Vatican Radio reported that Fr Paulo Dall'Oglio, a Jesuit priest, who has urged dialogue and rejected foreign military intervention since the start of the conflict, was departing in a few days at the request of the Syrian Catholic bishop.
What is happening in Syria is a "Muslim tragedy" in which Christians are involved, Fr Dall'Oglio told Vatican Radio.
He was expelled from Syria last November but managed to stay in the country.
Syria has a small but influential Christian minority that has traditionally enjoyed harmonious relations with the Muslim majority and with the regime of President Bashar al-Assad and his father and predecessor, Hafez.
It now lives in fear that the violence surrounding the uprising against Assad could degenerate into attacks on it by more radical elements among the Muslim population.
