Syria's opposition coalition has announced it would boycott this week's peace talks with the regime unless UN leader Ban Ki-moon withdraws an invitation to Iran to attend, The Australian reported.
"The Syrian Coalition announces that they will withdraw their attendance in G2 (Geneva II peace talks) unless Ban Ki-moon retracts Iran's invitation," Louay Safi, a spokesman for the Coalition, said on its twitter account.
Earlier, Mr Ban announced Iran would attend this week's Syria peace conference after it pledged to play a "positive and constructive role" in efforts to end the three-year-old war.
Mr Ban said he made a late invitation to Iran after intensive talks with Iran's Foreign Minister Mohammad Javad Zarif, who agreed to attend.
Iran's involvement means that all the key countries linked to the worsening war will now be at the opening of the peace conference in Montreux, Switzerland on Wednesday.
Talks between President Bashar al-Assad's government and the opposition are due to start in Geneva on Friday.
"Foreign Minister Zarif and I agree that the goal of the negotiations is to establish, by mutual consent, a transitional governing body with full executive powers," Mr Ban said.
"It was on that basis that Foreign Minister Zarif pledged that Iran would play a positive and constructive role in Montreux," the UN secretary-general added.
The United States and other Western powers had opposed Iran's attendance at the meeting as long as it refused to accept a communique adopted by the major powers in Geneva on June 30, 2012 calling for a transition government in Syria.
"I believe strongly that Iran needs to be part of the solution to the Syrian crisis," Mr Ban said.
Mr Ban said that as convener of the peace conference he has also invited Australia, Bahrain, Belgium, Greece, Luxembourg, Mexico, Netherlands, South Korea and the Vatican.
He said the extra countries would be "an important and useful show of solidarity in advance of the hard work that the Syrian government and opposition delegations will begin."