A senior member of Syria's Western-backed political opposition came out on Wednesday against Iranian participation in the Syrian peace talks in Vienna, saying their presence would undermine the political process. The United States has said that Iran, Syrian President Bashar Assad's main regional ally, is invited to tomorrow's talks and the semi-official Iranian ISNA news agency said Iranian Foreign Minister Mohammad Javad Zarif and his deputies will attend. About a dozen participants are expected, including Russia and Saudi Arabia, which back Assad and his opponents, respectively. Turkey will be represented by Foreign Minister Feridun Sinirlioğlu.Hisham Marwah, vice-president of the Turkey-based Syrian National Coalition, criticized any participation in the talks by Tehran, but stopped short of saying it would refuse participation itself if Iran was involved."Iran doesn't believe in the Geneva Communique. Involving it [Iran] in talks undermines the political process," he said, speaking of an internationally agreed document setting out guidelines for Syria's path to peace and a political transition.Asked whether the coalition would refuse to take part in talks, he said: "What's important now is not to refuse talks; it is important to express our concern. Iran has only one project – to keep Assad in power ... they don't believe in the principle of the talks."In January 2014, the opposition body refused to attend political talks in Switzerland unless the United Nations retracted its invitation to Iran. ISNA quoted Iranian Foreign Ministry spokeswoman Marzieh Afkham as saying that Deputy Foreign Ministers Hossein Amir Abdollahian, Abbas Araqchi and Majid Takht Ravanchi would accompany Zarif to Vienna.The Fars news agency said separately that Zarif had discussed Iranian participation in the talks with Russian Foreign Minister Sergei Lavrov by phone on Tuesday.Turkey and Saudi Arabia are in favor of Assad leaving office after a temporary process in which he would stay in office for a six-month period at most. Previously, Prime Minister Ahmet Davutoğlu spoke on a possible six-month transition period with Assad when the Syrian president was on a visit in Moscow, and said: "We need to dwell on formulas in which Assad leaves. I wish Assad could have stayed longer there [in Moscow], and the Syrian people could feel at ease, then the real transition period would have started." A senior diplomat also told a group of journalists that Ankara is ready to accept a transition period in which Assad remains in power symbolically for six months before leaving office. "Work on a plan for Assad's departure is underway. ... [Assad] can stay for six months, and we accept that because there will be a guarantee of his departure," he said. Syria is now in its fifth year of a civil war that has killed hundreds of thousands of people, contributed to a massive refugee crisis in Europe and has been complicated by the emergence of the Islamic State of Iraq and al-Sham (ISIS) and Russia's direct military intervention.Washington thinks that ousting Assad is essential for fighting ISIS with the moderate Syrian opposition. In a previous televised interview U.S. President Barack Obama said: "[W]hat we've learned is that as long as Assad remains in power, it is very difficult to get those folks to focus their attention on [ISIS]," adding that he was "skeptical from the get-go" about the notion of creating an army of moderate forces in Syria. Yet Washington's inconsistent policies in Syria since the beginning of the crisis have allowed Moscow to maneuver in favor of staunchly supporting Assad. Although Washington and Moscow apparently agreed on the anti-ISIS fight, Russian jets targetting moderate opposition groups, fighting regime forces and even civilians, has stirred tensions.