The sources said IRGC has been assigned to what they termed the "dirty work" in quelling the revolt against Assad. They said IRGC, aided by Hizbullah, was also participating in the identification and capture of rebels, including defecting soldiers.

IRGC was said to have supplied artillery and main battle tank shells to maintain the Syrian Army's drive against the rebels. The sources said Iran also transported tools for the torture of detained protesters.

"The Assad regime is receiving aid across its borders from its neighbors who owe allegiance to the Teheran regime," Syrian opposition spokesman Nasser Jaber said.

Jaber, spokesman for the National Resistance of Al Ahwaz, said Iran, through IRGC fronts, was helping smuggle billions of dollars to the Assad regime. At the same time, he said, the Iranian-sponsored Hizbullah was transporting weapons and fighters from Lebanon to Syria.

"Iran and its followers believe that the collapse of the Assad regime will put the expanding Iranian project in the region at risk," Jaber said.

The opposition has opened a dialogue with the Iranian regime to end support for Assad. Over the last month, leading Iranians, including President Mahmoud Ahmadinejad, have called on Assad to institute reform.

"I do not think the Syrian regime would have been able to survive militarily and economically over this long period without the aid of Teheran," opposition leader Bahiya Mardini, chairwoman of the Arab Committee for the Defense of Freedom of Expression, told the London-based daily A-Sharq Al Awsat.

But opposition sources doubted whether the Iranian leadership would abandon Assad. They said Assad has ensured Iranian domination of Lebanon as well as significant influence in Syria.

Iran also employed Syria as a base to control such proxies as Hamas, Hizbullah, Islamic Jihad and the Popular Front the Liberation of Palestine-General Command. The sources said Iran was believed to have deployed more than 4,000 fighters in Syria.

A Syrian military defector agreed. Walid Qushamie, a Syrian who fled the army in July, said he had encountered Hizbullah fighters in a Republican Guard base in Damascus.