Syria's political opposition has said it will withdraw from international peace talks scheduled this week unless the UN chief retracts an invitation to Iran, President Bashar al-Assad's main backer.

Ban Ki-moon, the UN secretary-general, said earlier on Sunday that he had invited Iran to attend the first day of talks on January 22 in Montreux, Switzerland, and that Iran had pledged to play a "positive and constructive role" if it was asked to participate.

Less than 48 hours since Syria's main political opposition group in exile, the Istanbul-based National Coalition, agreed to attend the talks, dubbed "Geneva 2", it threatened to withdraw.

"The Syrian Coalition announces that they will withdraw their attendance in Geneva 2 unless Ban Ki-moon retracts Iran's invitation," it said in a Twitter post quoting Louay Safi, National Coalition's spokesman.

Another senior National Coalition member, Anas al-Abdah, told Al Jazeera by phone that the body was "surprised" by the invitation to Iran, saying: "It is illogical and we cannot in any way accept it."

Syrian opposition groups and the US, which accuse Iran of supporting Assad with manpower and arms during the uprising against him, have long had reservations about the participation of Iran, although Ban and the UN special envoy on Syria, Lakhdar Brahimi, have long backed Iran's involvement.

The US suggested on Sunday it could support Iran's participation if it explicitly declares its support for a June 2012 plan for a political transition that the US says means Assad would have to step down.

"This is something Iran has never done publicly and something we have long made clear is required," Jen Psaki, State Department spokeswoman, said in a statement.

"If Iran does not fully and publicly accept the Geneva communique, the invitation must be rescinded."

Earlier this year the US said that Iran might play a role on the sidelines of the Syria peace conference in Montreux.

Iran dismissed the idea of being relegated to the sidelines, saying it was beneath Iran's dignity.

About 130,000 people have been killed and a quarter of Syrians driven from their homes in the civil war.

The uprising began with peaceful protests against 40 years of Assad family rule and has descended into a sectarian conflict, with the opposing sides armed and funded by Sunni Arab states and Shia Iran.

Assurance of support

Western and Gulf Arab states say they have been reluctant to support the idea of Iran participating at all because it is supporting Assad militarily and has never backed a plan for a political transition in Syria agreed at an international conference in Geneva in June 2012.

However, Ban, who was speaking at the UN headquarters, said he had spoken at length with Mohammad Javad Zarif, Iran's foreign minister, in recent days and that he believed Iran supported the Geneva 2012 plan.

"He has assured me that like all the other countries invited to the opening-day discussions in Montreux, Iran understands that the basis of the talks is the full implementation of the 30 June, 2012, Geneva communique," he said.

"Foreign Minister Zarif and I agreed that the goal of the negotiations is to establish by mutual consent a transitional governing body with a full executive powers," Ban said.

"It was on that basis that Foreign Minister Zarif pledged that Iran would play a positive and constructive role in Montreux."

"Therefore as convener and host of the conference I have decided to issue an invitation to Iran to participate," Ban said.

"Iran needs to participate as one of the important neighboring countries."

Ban said he expected Iran would issue a statement soon in response to his invitation.

He also said he had invited on Sunday a total of 10 additional countries to attend on January 22 - the Vatican, Australia, Bahrain, Belgium, Greece, Luxembourg, Mexico, the Netherlands, South Korea and Iran.

He made clear that the full negotiations between the government and opposition would begin in earnest on January 24 in Geneva.

The key players in the talks are Assad's government and opposition rebels.

The Islamic Front, an alliance of several fighting forces that represents a large portion of the rebels on the ground, said on Sunday it rejected the talks, further dampening hopes of success.

PHOTO CAPTION

A view of the Montreux-Palace, the hotel that will host the so-called Geneva II peace talks, in Montreux, on January 16, 2014.

Aljazeera