* Government delegation says "for us the round is over"
* Accuses opposition of setting preconditions for talks
* Mediator de Mistura has said round lasts until Dec. 15

Syria's top government negotiator said on Friday his team was quitting UN-led peace talks in Geneva and might not return next week, blaming the opposition's rejection of any role for President Bashar al-Assad in a transition.

Opposition groups met in Riyadh last month to hammer out a unified position ahead of the Geneva talks after two years of Russian military intervention that has helped Assad's government recapture all of Syria's main cities, which gave Damascus the upper hand after more than six years of war.
"As long as the other side sticks to the language of Riyadh 2 ..., there will be no progress," Bashar al-Ja'afari said after a morning of talks, adding that the Damascus government would decide if his delegation would return next week.
"For us (this) round is over, as a government delegation. He as mediator he can announce his own opinion," he said, referring to UN mediator Staffan de Mistura.
Pressed whether the government delegation would return to Geneva next week, Ja'afari replied: "Damascus will decide."
In a communique issued at the end of last month's round of talks, the opposition reiterated its position that Assad can have no role in a political transition: "The participants stressed that (this) cannot happen without the departure of ... Assad and his clique at the start of the interim period.
Ja'afari said the opposition statement was a kind of "mine" on the road to Geneva and the opposition had purposefully undermined the talks.
"The language with which the statement was drafted was seen by us, the Syrian government, as well as by too many capitals as a step back rather than progress forward, because it imposed a kind of precondition," he said.
"The language is provocative, irresponsible - politically speaking, and goes beyond the hopes of the Syrian people in this kind of talks."
Nasr Hariri, the opposition delegation chief, said on Friday said his side had come to Geneva for serious, direct negotiations with Assad's government. The opposition was to have talks with de Mistura later on Friday.
"We call on the international community to put pressure on the regime to engage with this process," he said in a statement.
Mistura said on Thursday the talks would run until Dec. 15, but that the government delegation might return to Damascus to "refresh and consult" before a resumption probably on Tuesday.