US Senator John McCain raised the prospect Sunday of possible armed intervention to protect civilians in Syria where a crackdown on pro-democracy protests has killed more than 3,000 people.
"Now that military operations in Libya are ending, there will be renewed focus on what practical military operations might be considered to protect civilian lives in Syria," McCain told a World Economic Forum meeting in Jordan.
McCain, the top Republican on the Senate Armed Services Committee, said Syrian President Bashar al-Assad's "regime should not consider that it can get away with mass murder.
Libya's ousted leader Moamer Kadhafi, who was captured and killed on Thursday, "made that mistake and it cost him everything," he said.
"There are even growing calls among the opposition for some foreign military intervention. We hear these pleas for assistance. We are listening to and engaging with the (opposition) National Council," he added.
The United Nations has said more than 3,000 people, including 187 children, have been killed in a fierce crackdown on dissent since mid-March.
"The Syrian revolution may now be entering a new phase. The opposition has formed the Syrian National Council seeking to better organise itself. There are increasing reports of defections from the army," said McCain.
"More Syrians appear to be taking up arms against the regime."
McCain charged that "dark forces in this region, especially in Iran, are working harder than ever to hijack the promise of what many are calling the Arab Spring.
"These concerns are real and legitimate and merit our vigilance."
US-Iran tensions have been running high since Washington accused Tehran of being behind an alleged plot to assassinate the Saudi ambassador in Washington. Iran has denied any involvement.
McCain held talks with key US ally King Abdullah II on Middle East issues, Jordan's state-run Petra news agency reported.
The United States and Jordan on Sunday signed a $250-million agreement under a "small and medium enterprise loan guarantee programme" to support the cash-strapped kingdom's economy.