Sen. John McCain will call for the launch of U.S. air strikes against Syria's army, according to prepared remarks obtained by Foreign Policy's Cable blog of a speech the Arizona Republican is expected to deliver Monday on the Senate floor.

McCain has been among the most vocal proponents of backing rebels fighting the government of Syria's President Bashar al-Assad. The 2008 Republican presidential candidate has said the United States should arm the dissidents or provide material support such as medical supplies.

President Barack Obama's administration has been circumspect, with Secretary of State Hillary Clinton seeking a diplomatic solution after China and Russia vetoed a United Nations Security Council resolution aimed at stopping the violence inflicted by Assad's forces.

But as the onslaught has continued, leading rebels to flee part of the besieged city of Homs, McCain will become the first U.S. lawmaker to press for direct military assistance to the rebels.

Providing military assistance to the Free Syrian Army and other opposition groups is necessary, but at this late hour, that alone will not be sufficient to stop the slaughter and save innocent lives, McCain will say, according to the transcript. The only realistic way to do so is with foreign airpower.

McCain will cite requests for aid from various Syrian opposition forces, including the Free Syrian Army and the Syrian National Council, in urging the U.S. military to do more to protect civilian populations in the Middle Eastern nation.

To be clear: This will require the United States to suppress enemy air defenses in at least part of the country, McCain will say. The ultimate goal of airstrikes 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. The safe havens can also be used to funnel medical and humanitarian supplies to civilians, according to McCain.

While Assad's government has denied that it is attacking civilians, observers and journalists have described indiscriminate bombing of civilian areas. U.S. Ambassador Robert Ford, who fled Syria amid rising violence, said Assad's army initiated assaults on civilian areas. The United Nations has accused Syrian security forces of crimes against humanity.

McCain will also draw a parallel to Libya, where the Obama administration sanctioned air strikes to aid rebels seeking to topple dictator Moammar Gadhafi. The kinds of mass atrocities that NATO intervened in Libya to prevent in Benghazi [in Libya] are now a reality in Homs, McCain's remarks read.

Experts point out that Syria's army is larger and more sophisticated than Libya's, complicating a U.S. military intervention. Also, the Syrian military is stocked with Assad loyalists and hasn't seen the kind of mass defections that weakened Gadhafi's forces in Libya.