DAMASCUS, Syria – Syrian opposition figures who reject foreign intervention in Syria’s 18-month conflict called for the ouster of President Bashar Assad at a rare meeting Sunday in the nation’s capital. The gathering was tolerated by the regime in an apparent attempt to lend credibility to its claims that it remains open to political reform despite its bloody crackdown on dissent.

A senior former Assad ally, meanwhile, said Iran is providing massive support for the embattled Syrian regime.

“Iranians are active in leading positions in the military,” former Syrian Prime Minister Riad Hijab, who defected to the opposition last month, told the German daily Frankfurter Allgemeine Zeitung. “We’re not only talking about military aid, but also logistical and economic support” by Iran.

Earlier this month, the top commander of Iran’s powerful Revolutionary Guard said the elite unit has high-level advisers in Syria. Iran is also believed to be sending weapons to Syria.

In recent weeks, Assad’s military has escalated air strikes and shelling of civilian areas to put down an uprising that began in March 2011 with peaceful protests but has since devolved into a civil war. Activists say close to 30,000 people have been killed.

Sunday’s opposition conference was attended by diplomats from Iran, Russia and China, Assad’s main allies. It was likely to be viewed as a cosmetic gesture by Syrian rebels and their many backers in the international community.

The loose network of Syrian rebel groups and the political opposition outside Syria believe Assad can’t be trusted to negotiate reform or a peaceful transfer of power, and call for foreign military intervention to break the stalemate in the conflict.

The United States and its allies have refrained from such action, partly because of international divisions over Syria and fears of a wider conflict. The opposition figures who met in Damascus are open to the idea of a political settlement, even though the conflict so far has eluded all attempts at mediation.

Assad’s government tightly restricts criticism in areas it controls, and security was tight for Sunday’s one-day conference at a Damascus hotel, attended by dozens of people. Streets leading to the hotel were blocked off, plainclothes security agents patrolled the perimeter and participants passed through security checks.

A bomb hidden in a black bag exploded on a footbridge in downtown Damascus, less than a mile from where Sunday’s opposition conference was held. Two people suffered slight injuries, witnesses said.

Sunday’s meeting was organized by the National Coordination Body for Democratic Change in Syria, or NCB, an umbrella for 16 opposition groups.

On Thursday, two senior NCB leaders disappeared after landing at Damascus International Airport, along with a friend who was to pick them up, and the NCB has blamed the regime for the disappearance. The government claimed the three were kidnapped by “terrorist groups.”

Despite the incident, the group said participants agreed on the idea of “overthrowing the regime with all its symbols” while emphasizing the need for “peaceful struggle to achieve the goals of the revolution.”

“It’s our right to meet here in the capital to express our views without being subject to dictates and pressures or to be forced to make concessions,” said the NCB’s head, Hassan Abdul-Azim, who spent long years in Syrian prisons for his opposition role.

The strong language may be aimed at gaining credibility among Syrians who despise the regime but are weary of civil war.

NCB leaders accuse the rebels and the Syrian National Council, an opposition group based outside Syria, of being beholden to Turkey, which shelters defected Syrian generals and opposition figures, as well as Gulf Arab countries that support the rebels.

The rebels, in turn, accuse the NCB of being cut off from grass-roots opposition fighters on the ground. Many rebels look askance at any political plan short of Assad’s ouster.