WASHINGTON U.S. Defense Secretary Leon Panetta said on Wednesday he had no knowledge of the United States supplying Stinger missiles to Syrian rebel forces, after Moscow said the rebels had acquired the U.S.-made surface-to-air missiles.
Asked about reports that the rebels had such weapons, Panetta declined comment, saying: "I don't know what the reports are - and I certainly don't know of us providing any such missiles in that area."
Russia's top military officer, general staff chief Nikolai Makarov, said Russia's military had learned that rebel forces "have portable missile launchers of various states, including American-made Stingers.
"Who supplied them must still be determined," Interfax news agency quoted him as saying.
A U.S. defense official, speaking on condition of anonymity, told Reuters the United States was unable to confirm that the rebels had acquired U.S. Stingers.
Stinger missiles would help bring down warplanes and helicopters which have bombed residential areas where rebels are hiding. But in contrast to the Libya crisis last year, the West has shown little appetite to arm the Syrian rebels, worried that weapons would fall into the hands of Islamic militants.
More than 32,000 people have been killed in the conflict, which began with peaceful pro-democracy protests in March 2011 before descending into civil war as repression increased.
The question of whether to arm the rebels has become an issue in the U.S. presidential election, with Republican candidate Mitt Romney accusing President Barack Obama of failing to show leadership.
In their debate on Monday, Romney said the United States should work with partners to organize the Syrian opposition and "make sure they have the arms necessary to defend themselves."
Obama said Romney was wrong to suggest that giving rebels heavy weapons "is a simple proposition that would lead us to be safer over the long term."
Opposition activist footage has shown rebels carrying surface-to-air missiles made by the former Soviet Union, but footage of Stingers has yet to appear.
Russia, which has supported Assad through the conflict, sold his government $1 billion worth of weapons last year and has made clear it would oppose an arms embargo in the U.N. Security Council.
(Editing by Paul Eckert and Vicki Allen)