The United States is worried Russia may be sending Syria attack helicopters and views Russian claims that its arms transfers to Syria are unrelated to the conflict there as "patently untrue," U.S. Secretary of State Hillary Clinton said on Tuesday.  

The comments came as the Pentagon found itself on the defensive for doing business with Russian state arms exporter Rosoboronexport, given concerns in Congress about the firm's role in arming the Syrian regime.  

"We have confronted the Russians about stopping their continued arms shipments to Syria. They have, from time to time, said that we shouldn't worry - everything they are shipping is unrelated to their (the Syrian government's) actions internally," Clinton said, addressing a forum in Washington.   

"That's patently untrue."   

Clinton did not offer any details about the source of her information about Russia's possible shipment of attack helicopters to Syria, saying only: "We are concerned about the latest information we have that there are attack helicopters on the way from Russia to Syria."   

She said such a sale "will escalate the conflict quite dramatically."   

State Department spokeswoman Victoria Nuland told reporters that Clinton was concerned about helicopters now en route to Syria and not about possible past sales of Russian-origin attack helicopters to Syria.   

She said that she could not elaborate or speculate on the source of Clinton's information.   

Pentagon spokesman Captain John Kirby said he had no knowledge of a new helicopter shipment but acknowledged that Assad's regime was turning to helicopters to stage attacks.   

"We know that the Assad regime is using helicopter gunships against their own people," Kirby said.   

Asked whether Russia's resupply of military equipment to  Syria was enabling the Syrian armed forces to continue the killings, Kirby said: "To the degree that the Syrian armed forces use that resupply to kill their own people, then yes."

The Syrian government's use of Russian-made arms has thrown a spotlight on the Pentagon's purchase of Russian helicopters for the Afghan military, which the United States is building up so that it can take over security as American troops withdraw.

REUTERS