(Reuters) -- Syria's government delegation quit U.N.-led peace talks in Geneva on Friday and said it might not return next week, blaming the opposition's rejection of any role for President Bashar al-Assad in any interim post-war government.
"For us (this) round is over, as a government delegation. He as mediator he can announce his own opinion," government chief negotiator Bashar al-Ja'afari said after a morning of talks, referring to U.N. mediator Staffan de Mistura who made no immediate comment.
"As long as the other side sticks to the language of Riyadh 2 ..., there will be no progress," Ja'afari said.
He was referring to a position adopted by Syrian opposition delegates at a meeting in Riyadh last week, in which they stuck to their demand that Assad be excluded from any transitional government.
Previously there had been some speculation the opposition could soften its stance ahead of this week's Geneva negotiations, in response to government advances on the battlefield.
The Syrian civil war, now in its seventh year, has killed hundreds of thousands of people and driven 11 million from their homes. So far all previous rounds of peace talks have failed to make progress, faltering over the opposition's demand Assad leave power and his refusal to go.
Pressed whether the government delegation would return to Geneva next week, Ja'afari replied: "Damascus will decide."
Ja'afari said the statement insisting Assad leave power that was adopted by the opposition in Riyadh ahead of this week's peace talks was a "mine" on the road to Geneva, and the opposition had purposefully undermined the negotiations.
"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."
The opposition, which held brief talks separately later with U.N. officials, rejected the charge that it was seeking to undermine the talks, and said it sought a "political solution".
"We have come to this round with no preconditions," opposition spokesman Yahya al-Aridi told reporters on arrival.
"Now, not coming back is a pre-condition in itself. It's an expression or a reflection of a responsibility towards people who have been suffering for seven years now," Aridi said.
Nasr Hariri, the opposition delegation chief, said earlier on Friday that his side had come to Geneva for serious, direct negotiations with Assad's government. So far, government and opposition delegations have not negotiated face-to-face in any Syrian peace talks but have been kept in separate rooms.
"We call on the international community to put pressure on the regime to engage with this process," Hariri said in a statement.
De 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.