U.S. officials say Iran is increasingly active in backing Syrian President Bashar al-Assad's campaign of violence against his own people.
As opposition attacks against the Syrian government grow, U.S. officials say Damascus increasingly seeks help from Iran to hold onto power.
Central Intelligence Agency chief David Petraeus told U.S. lawmakers Iran helps Syria because it is fighting to maintain its position in the region.
"Clearly the loss of Syria as a logistics platform, a line of communication into Lebanon to support Hezbollah, would be a substantial setback for Iran in its efforts to use Hezbollah as a proxy, and that is indeed why the Revolutionary Guards corps Quds Force is so engaged in trying to prop up Bashar al-Assad right now," Petraeus said.
Syrian opposition member Samir Nassar says Iran must stop backing President Assad.
"The Syrian National Council is against the Iranian regime's stance on Syria," he said. "While Syrians are being killed, we urge Iran to stop helping the Syrian regime.?
Analyst Marou Innocent from the Cato Institute research group says Iran and its Hezbollah allies face an uncertain future in Syria.
?We have seen actually many Syrian protesters begin to burn Hezbollah flags, Iranian flags," said Innocent. "So there is again a fissure within Syria. These are former allies of the Assad regime, and the Assad regime stood up the West and to the United States. Now, again, we see the fracturing of those coalitions within Syria and a depreciation of Hezbollah's influence and Iran's influence within the country.?
But it?s not certain that Iran would lose all influence in Syria after President al-Assad.
U.S. Institute of Peace Middle East analyst Steve Heydemann notes some Syrian nationalists in the opposition value their ties with Tehran.
?If Syria were somehow to slip out of the Iranian column, it would be an enormous blow to Iran's ability to project its influence regionally," said Heydemann. "But again, that is only if we imagine that an alternative Syrian government would re-orient Syria's foreign policy. And I do not think we can take that for granted.?
It is not only Iran's support for Hezbollah that might suffer from a change of government in Damascus. Tehran could also find it harder to supply arms and money to Hamas in Gaza, at a time Iran's economy is declining under sanctions against its nuclear program.