Lakhdar Brahimi, the United Nations and Arab League envoy, says a proposed peace conference to end the 2 1/2-year-old conflict in Syria could not be held if the Syrian opposition refuses to participate.
Brahimi was speaking on November 1 at the end of a five-day visit to Damascus.
The opposition National Coalition plans to meet in Turkey next week to make a final decision on its participation.
Syrian opposition groups are split on whether to attend the conference in Geneva proposed by the United States and Russia.
In an interview with the Reuters news agency on October 31, Russian Prime Minister Dmitry Medvedev criticized the opposition for demanding assurances that President Bashar al-Assad step down as a condition for the talks.
Medvedev said Assad would need "guarantees" on his fate before he would agree to step down.
Based on reporting by AFP, dpa, and Reuters