The United States on Thursday accused Iran of playing a "nefarious" role in the Syria conflict, one that strengthens the case for President Bashar al-Assad to be forced out of office.
Susan Rice, US ambassador to the United Nations said the alliance of Iran, Lebanese Hezbollah and Assad's government -- a group that boasts of being the Middle East's "an axis of resistance" -- was "bad for the region."
Rice was speaking to NBC television shortly after Assad met a top Iranian envoy in his war-torn capital this week and as Tehran hosted a conference on the conflict designed to shore up the beleaguered Syrian regime.
"They view this as an axis of resistance along with Hezbollah, so there is no question that Iran is playing a nefarious role, not only in Syria but more broadly in the region, actively supporting the Assad regime," she said.
"One of the reasons why we are quite clear that the end result must be and will be the departure of Assad, is because this alliance, so to speak, is bad not only for Syria, but it is bad for the region and bad for our interests."
At its hastily-arranged international conference, Iran appealed to Syria's government and armed opposition to open peace talks.
Foreign Minister Ali Akbar Salehi told diplomats from Russia, Pakistan, Afghanistan, Cuba, Venezuela and other nations that Iran opposes "any foreign interference and military intervention in resolving the Syrian crisis."
Rice said the United States was wary about imposing a Libya-style no fly zone over Syria even though it wanted to increase support for the opposition.
Signup to our newsletter and follow us on Facebook and Twitter!
Some Syrian opposition rebels and US politicians have called for a no fly zone and Rice said "none of these potential options have been ruled out."
But she told NBC "the reality is that a no-fly zone isn't a simple proposition, it would ultimately involve putting boots on the ground and it would be a very different circumstance than we saw in Libya."
The US envoy said "the Syrian air defenses are among the most sophisticated in the world. Their military is quite a different beast."
Last year, United States, Britain and France led a coalition which patrolled a no-fly zone over Libya. The mission later escalated into a NATO-led bombing campaign in support of the rebels that eventually overthrew Moamer Kadhafi.
Russia, China and other UN Security Council countries say they were tricked into accepting the resolution which gave UN approval to the action.
Russia and China have blocked three Security Council resolutions which threatened or even hinted at sanctions against Assad's government.
Rice said the United States is "actively looking at ways to strengthen the opposition: materially and financially and substantively and politically and that is already beginning to show some progress on the ground."
The ambassador admitted that fighting between Assad's forces and rebels is intensifying but insisted the "momentum is shifting clearly in favor of the opposition."
"The defections are mounting, the economic pressure is mounting, the political isolation of the Assad is increasing," she said.