U.S. State Department is acknowledging that the Russian helicopters Secretary of State Hillary Rodham Clinton said represented an escalation in the Syrian conflict were actually returning to Syria after being refurbished and are not new tools against Syrian opposition groups.

State Department spokeswoman Victoria Nuland says the U.S.¬ is nevertheless concerned that the helicopters will be used by President Bashar Assad's regime to kill civilians.

"Whether they are new or whether they are refurbished, the concern remains that they will be used for the exact same purpose that the current helicopters in Syria are being used and that is to kill civilians,” Nuland said.

She says three helicopters are on the way to Syria after being out of commission for at least six months. And she says that's "three more that can be used to kill civilians."

Clinton accused Russia earlier of escalating the crisis by sending helicopters, but didn't say they were refurbished.

Nuland on Thursday declined to say why the State Department didn't divulge tha detail earlier.