Syria Geneva II peace talks witness bitter exchanges
Syria's government and main political opposition have traded bitter accusations on the first day of a major peace conference in Switzerland.
The opposition and US said President Bashar al-Assad had no legitimacy and must step down from power.
Syria's foreign minister had a terse exchange with the UN's Ban Ki-moon over the length of his speech and said only Syrians could decide Mr Assad's fate.
The conflict has left more than 100,000 dead and millions displaced.
The summit is discussing the Geneva communique which lays out a political transition plan for Syria.
Wednesday's initial meeting, involving speeches from 40 or so foreign ministers - has now ended. The direct talks are scheduled to begin in Geneva on Friday.
At a fractious evening news conference, during which there were repeated calls for calm, Mr Ban spoke of the suffering in Syria, saying: "Enough is enough. The time has come to negotiate."
He said that "the really hard work begins on Friday", adding: "We have a difficult road ahead, but it can be done and it must be done."
Mr Ban dwelt on the Geneva communique, which calls for a transitional government in Syria, saying he was disappointed with the attitudes of both the Syrian government and its ally, Iran.
UN mediator Lakhdar Brahimi said he would speak to the Syrian government and opposition delegations separately on Thursday and that he hoped both teams would meet in the same room on Friday.
This would be the first face-to-face meeting between the Syrian government and the main opposition - the National Coalition - since the conflict began in 2011.
At his press conference, US Secretary of State John Kerry stressed that the Geneva communique and its call for political transition was the paramount focus of the summit.
"Every delegation, with one exception, embraced the Geneva communique," he said, referring to the Syrian government.
"No-one has done more to make Syria a magnet for terrorists than Bashar al-Assad," Mr Kerry said. "You cannot save Syria with Bashar al-Assad in power."
A member of the Syrian team, UN ambassador Bashar Jaafari, criticised the exclusion of Iran from the meeting, and condemned many of Wednesday's speeches as "provocative and repetitive statements based on hatred towards the Syrian government".
He also accused Gulf states of "inciting terrorism" in Syria.
The BBC's Paul Wood, in Montreux, says there were some extraordinarily ill-tempered scenes and some very direct language at the morning meeting.
Syria's Foreign Minister Walid Muallem said some states attending the talks had "Syrian blood on their hands" and called the opposition "traitors".
Addressing Mr Kerry, he said: "No-one in the world has the right to confer or withdraw the legitimacy of a president, a constitution or a law, except for the Syrians themselves."
Mr Muallem ran far over the allotted 10-minute slot for each speaker, ignoring Mr Ban's attempts to intervene.
"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 US state department condemned Mr Muallem's remarks as "inflammatory rhetoric", and urged the government to take "real, concrete steps to increase humanitarian access and improve the lives of the people suffering the most".
The head of the National Coalition, Ahmad Jarba, said the Syrian government must sign up to a deal to transfer powers from Mr Assad.
Mr Jarba said that this would be "the preamble to Bashar al-Assad's resignation and his trial alongside all the criminals of his regime".
He added: "For the Syrians, time is now blood."
Mr Jarba displayed a photograph taken from a report by three war crimes investigators which alleged "systematic" torture and execution of opposition detainees in Syria. The report was released on Tuesday but dismissed as not credible by Damascus.
Our correspondent says that when the talks go behind closed doors there will perhaps be a more constructive tone - with discussion of practical matters such as ceasefires and access for humanitarian aid.
Russian Foreign Minister Sergei Lavrov said the talks "will not be simple, will not be quick", but that there was "a historic responsibility on the shoulders of all participants".
He also repeated his insistence that Iran should be involved.
The UN withdrew its invitation to Iran this week over its refusal to back the Geneva communique.
Iran's President Hasan Rouhani said on Wednesday that the "lack of influential players" attending meant he doubted "its ability to resolve the Syria crisis".