BEIRUT — Syria's main, Western-backed opposition said Monday it will not attend the U.N.-hosted peace talks in Geneva this week aimed at ending the country's civil war if Iran comes to the gathering.

Ahmad Ramadan, a senior member of the Syrian National Coalition, said the opposition is "suspending" its participation because Iran has forces in Syria and is "invading" the country.

The comments came hours after the United Nations invited Iran to attend an international meeting of foreign ministers in the Swiss city of Montreux ahead of the first direct peace talks between the warring Syrian sides.

The remarks also further decreased already low expectations of major breakthroughs at the conference, which was to bring for the first time ever representatives of Syria's government and its opponents face-to-face in an international setting.

Diplomats and political leaders have acknowledged that the prospects of bringing a halt to a conflict that has killed more than 130,000 people and touched off the worst humanitarian crisis in decades any time soon are slim at best.

Ban said he had issued the invitation to Iran after "speaking at length in recent days" with Iranian Foreign Minister Javid Zarif, who had "pledged that Iran would play a positive and constructive role in Montreux."

The aim of the conference, dubbed Geneva 2, is to agree on a roadmap for Syria based on one adopted by the U.S., Russia and other major powers in June 2012. That plan includes the creation of a transitional government and eventual elections.

Iran is Syrian President Bashar Assad's strongest regional ally, extending him billions of dollars in credit since the crisis began in March 2011. The United States, Saudi Arabia and several countries in the Persian Gulf suspect Tehran is also shipping him weapons.

"We informed Ban Ki-Moon in the past that the Coalition will not attend Genva 2 if Iran was invited," Ramadan said by telephone from Istanbul. "We consider Iran a country that is invading Syria and sending militias, whether it's Revolutionary Guards or Hezbollah."

In 2012, the chief commander of Iran's powerful Revolutionary Guard, Gen. Mohammad Ali Jafari, said the unit had high-level advisers in Syria but denied it has fighters there. More recently, however, analysts say that Iranian troops and commanders have taken on a more direct role in the conflict.

Lebanon's Iran-backed Hezbollah fighters openly joined the war in Syria last year fighting along with Assad's forces.

It remained unclear how definitive the Syrian opposition pullout was and how far it would go to get Iran away from Geneva.

"If the situation does not change, the Coalition will not be" at the talks this week, Ramadan said.