Syria's President Bashar al-Assad enjoys the support of his people and can continue to count on his ally Iran as he battles an armed rebellion in his country, a senior Iranian official was quoted as saying on Sunday.

Iran has steadfastly supported Assad in his 17-month-long bid to hold onto power against armed Syrian rebels, accusing regional powers including Turkey and Qatar and the West of fomenting unrest in Syria because of its opposition to Israel.

Saeed Jalili, secretary of Iran's Supreme National Security Council and a representative of Iran's ultimate authority, Supreme Leader Ali Khamenei, said on Sunday that Syria was a "strong fortress of resistance" against the West and Israel and was thus being targeted for overthrow.

"How could Assad have lasted this long? Isn't it because he's leaning on popular support?," Jalili was quoted as saying by Iran's Mehr News Agency, which on Sunday published what it said was a transcript of an interview of Jalili with the Arabic-language channel Al-Mayadeen.

"We're not saying that no one is opposed to him," Jalili added. "But at the end of the day the will of the people is with him."

Jalili, also Iran's chief negotiator in its dispute with major world powers over its nuclear programme, reiterated Iran's position that Syrian opposition and the government should sit down to negotiate and free elections should be held rather than Assad's abrupt departure from power.

Iran has denied that it has sent forces from its elite Islamic Revolutionary Guard Corps to help put down the uprising, while accusing Turkey and Qatar of aiding the rebels.

Earlier this month 48 Iranians were captured by rebels near Damascus on suspicion of being military personnel, though Iran insists they are religious pilgrims.

Jalili said he "100 percent" denies Iran's involvement in Syria, Mehr reported.

"It's been one year that they have worked toward the downfall of the Assad government, but they haven't gotten anywhere with their efforts," Jalili was quoted as saying. "We don't place any importance on such lies and the deceptions of news agencies, whose goal is to hurt relations between Iran and Syria."