Top Republican Senator John McCain on Monday called for US air strikes on Syrian forces to protect population centers and create safe havens for opponents of the regime.

McCain, who lost to President Barack Obama in the 2008 election, said while the White House "deserves a lot of credit" for helping to build global efforts to isolate President Bashar al-Assad, it was time for a "new policy."

The speech by McCain came as Syrian forces bombarded the city of Rastan, pursuing a deadly crackdown on anti-regime protesters that erupted a year ago, and which the United Nations says has claimed more than 7,5 00 lives.

"Time is running out," McCain -- a hawk on both Syria and Iran -- said in remarks on the floor of the Senate.

"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," he said.

"The only realistic way to do so is with foreign air power," he said, urging the United States to join with Arab countries, as well as willing partners in the European Union and NATO, especially Syria's neighbor Turkey.

At the request of the Syrian opposition, McCain said, "the United States should lead an international effort to protect key population centers in Syria, especially in the north, through air strikes on Assad's forces."

"To be clear: This will require the United States to suppress enemy air defenses in at least part of the country."

So far, neither the Obama administration nor Democratic lawmakers have raised the possibility of military action in Syria.

While he lauded Obama's efforts targeting Assad, and said he understood the administration was "reluctant to move beyond diplomacy and sanctions," he also said the current approach did not reflect realities on the ground.

"Unfortunately, this policy is increasingly disconnected from the dire conditions on the ground in Syria, which has become a full-blown state of armed conflict," he said.

"Foreign capitals across the world are looking to the United States to lead," McCain said, blasting Russia, China and Iran for what he called their "shameless support" of Assad.

"But what they see is an administration still hedging its bets -- on the one hand, insisting that Assad's fall is inevitable, but on the other, unwilling even to threaten more assertive actions that could make it so."

"The time has come for a new policy," McCain said.

"Are there dangers, and risks, and uncertainties in this approach? Absolutely."

McCain argued it would be a "strategic and moral defeat" for the United States if Assad succeeds in clinging to power, and said military action was needed to drive a negotiated transition.

"What opposition groups in Syria need most urgently is relief from Assad's tank and artillery sieges in the many cities that are still contested," he said.

He said the safe havens protected by air power would allow the Free Syrian Army and other armed groups to train and organize themselves, and enable the delivery of humanitarian and military assistance.

"They have earned our respect, and now they need our support to finish what they started. The Syrian people deserve to succeed, and shame on us if we fail to help them."

McCain had already spoken in favor of sending arms to the Syrian opposition. Last year, he was a key backer of US participation in the foreign air campaign on Libya, which eventually helped bring about the downfall of Moamer Kadhafi.