Ranking U.S. Senator John McCain on Monday called for U.S.-led air strikes on Syrian forces to protect key population centers in the Arab nation.

"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," the Republican from Arizona said in a Senate floor speech.

"The only realistic way to do so is with foreign air power," he argued. "To be clear: This will require the United States to suppress enemy air defenses in at least part of the country."

The Obama administration favors a diplomatic resolution to the Syrian crisis for now, calling on Syrian President Bashar al-Assad to step down to make way for a peaceful transition in his country.

"The United States should lead an international effort to protect key population centers in Syria, especially in the north, through airstrikes on Assad's forces," McCain stated.

He said safe havens should be established and defended for delivering humanitarian and military aid in Syria.

The senator, who lost to Barack Obama in the 2008 presidential election, proposed last month that the Syrian opposition should be armed, an idea rejected by the Obama administration.