The United Nations Secretary General Ban Ki-Moon has told the two sides in Syria's civil war that the time has come for earnest negotiations to end the conflict.
Speaking after the first day of a peace conference in Switzerland, Mr Ban said Syrians must come together to save their country and protect their children.
Earlier, Syrian government and opposition delegations faced each other for the first time since the start of the conflict nearly three years ago. They traded bitter accusations, highlighting sharp divisions between them.
The Syrian opposition and the United States said President Bashar al-Assad had no legitimacy and must step down from power, the BBC reports.
Syria's Foreign Minister Walid Muallem called the opposition traitors and foreign agents, and said the real issue in Syria was terrorism by Sunni militant groups backed by countries in the Gulf.
He also had a terse exchange with the chairman, UN Secretary-General Ban Ki-moon, refusing to cut short his lengthy speech and saying only Syrians could decide Mr Assad's fate.
"You live in New York. I live in Syria," Mr Muallem told the UN Secretary-General. "I have the right to give the Syrian version here. After three years of suffering, this is my right."
The summit in Montreux is discussing a political transition plan for Syria and was hearing from about 40 foreign ministers on Wednesday before direct talks were scheduled to begin in Geneva on Friday.
UN mediator Lakhdar Brahimi said he was unsure whether the two sides would sit together at the next meeting in Geneva.
"Tomorrow I'm going to meet them separately and see how best we can move. Do we go straight on Friday into one room and start discussing, or do we talk a little bit more separately? We have no illusion that it is going to be easy."