UN Secretary General Ban Ki-moon has urged Syria's warring sides to seize the opportunity to resolve their conflict.
Mr Ban was speaking on teh opening day of a peace conference in Switzerland.
He told delegates "After nearly three painful years of conflict and suffering in Syria, today is a day of hope. You have an enormous opportunity and responsiblity to render a service to the people of Syria."
The UN chief urged the warring sides, who are meeting for the first time since the start of the conflict in March 2011, to act urgently to end the crisis estimated to have killed more than 130,000 people and forced millions to flee their homes.
"All people are looking to you gathered here today to end the unspeaking suffering," Ban said, also calling on the representatives of some 40 nations and international organisations gathered at the conference to step up.
International powers must "do everything within their power to help them achieve these goals," he said.
"How many more will die in Syria... if this opportunity is lost? Ban asked.
"There is no alternative to ending the violence... Let us prove to all that the world is able to unite," he said.
