US Sen. John McCain of Arizona said on Monday the United States should take the lead in an allied air campaign against Syrian armed forces.
"The ultimate goal of air strikes should be to establish and defend safe havens in Syria, especially in the north, in which opposition forces can organize and plan their political and military activities against Assad," McCain, an influential Republican, said in remarks on the Senate floor.
McCain has previously called for efforts to arm the Syrian opposition. But he said on Monday the help Syrian rebels needed most urgently was "relief from Assad's tank and artillery sieges in the many cities that are still contested" in Syria.
The battered city of Homs is "lost for now," but other cities are not, the 2008 Republican presidential nominee said.
The Obama administration has thus far stressed seeking a political solution to the crisis. Last month, the White House said it did not rule out "additional measures" if a political solution turned out to be impossible.