WASHINGTON — Republican US Senator Dick Lugar, one of his party's elder statesmen on foreign policy, cautioned Tuesday against providing US aid to Syria's opposition "at this point."

"I think for the time being we should back our ambassador, who I think is doing a great job of witnessing what is occurring, informing us and European countries or others who are interested," Lugar told reporters.

"But I would not advocate action beyond that at this point," said the senator, who had been asked what help Washington could provide to the opposition to President Bashar al-Assad amid a bloody months-long crackdown.

Lugar, the top Republican on the Senate Foreign Relations Committee, warned that it would be "very difficult" to identify potential recipients of US help among the "tribes, regional groups of all sorts" and other foes of the regime.

"We're not really prepared to pick and choose winners and losers in that situation," said the lawmaker.

His comments came as Syria's opposition urged the global community to act, deploring its failure to stop "massacres," ahead of a showdown at the UN Security Council over a resolution aimed at halting the violence.