Moderate Syrian rebels backed by the West threatened to pull out of this week's scheduled peace conference if the United Nations does not withdraw an invitation to Iran.

UN secretary-general Ban Ki-moon said that he had invited Iran to the talks in Montreux, Switzerland, after Tehran pledged to play a "positive and constructive role" in efforts to end Syria's three-year civil war.

But the Syrian National Coalition said furiously that it would withdraw from the negotiations unless the disputed invitation to Iran was retracted.