The Syrian National Dialogue Congress in Sochi is postponed until February, Russian news agency RIA reported Monday, citing diplomatic sources.

The event, called the Syrian Congress on National Dialogue, was initially to be held in November but some opposition groups rejected the idea of the meeting, initially proposed by Russian President Vladimir Putin.

The congress marks efforts by Turkey, Russia and Iran to advance a political solution towards ending Syria's six-year-long war that has killed hundreds of thousands of people and forced millions to flee in the worst refugee crisis since World War Two.

Putin and Erdoğan said the congress aims at realizing constitutional reform and holding free elections observed by the U.N. while ensuring an "inclusive and fair" political transition in the country.

The United Nations is to resume the peace talks between the government and the Syrian opposition in Geneva on Tuesday.

The opposition had announced last week it was prepared to enter into direct talks with the government without preconditions, although some opposition figures have demanded regime leader Bashar Assad relinquish power once the country enters a transitional period.

The government has not yet named its delegation to the talks and a the pro-regime Al-Watan daily said the state's team is not expected to head to Geneva on Monday as scheduled, claiming the opposition demands for Assad to leave are "hidden conditions."