Syria’s opposition says it will withdraw from this week’s peace talks in Switzerland unless an invitation to Iran is retracted.

The announcement follows UN Chief Ban Ki-moon’s offer to Tehran to attend the first day of the talks.

The preliminary talks will open in Montreux on Wednesday and then continue in Geneva two days later.

“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, adding: “it was on that basis that Foreign Minister Zarif pledged that Iran would play a positive and constructive role in Montreux.”

The decision by the Syrian National Coalition which on Saturday finally agreed to take part has thrown uncertainty around the talks.

The US has also stipulated Iran must endorse the 2012 Geneva communique detailing Syria’s political transition process if it is to attend.

Syrian opposition figures had earlier expressed reluctance to go to Switzerland unless President Bashar al-Assad was excluded from any future transitional government.

Assad has recently been quoted as saying he has no intention of quitting.