Syria's government and opposition have agreed on an agenda for a third round of peace talks in Geneva, despite disappointment at the little progress achieved as the second round came to an end.

No date was set for the negotiations to resume, and dispute overshadowed the potential talks as the two sides debated the order in which the agenda's four topics will be discussed: combating violence, transitional government, national institutions and national reconciliation.

United Nations mediator Lakhdar Brahimi proposed devoting the first day to a discussion of violence and "terrorism," and the second to the issue of a transitional governing body.

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"I apologise to the Syrian people ... I apologise to them that in these two rounds we haven't helped them very much," Brahimi said.

He urged both sides to "reflect" and return ready to make progress in the anticipated third round.

"A third round without talking about transition would be a waste of time," opposition spokesman Louay Safi told reporters in Geneva, after the negotiations ended in failure.

Al Jazeera's James Bays, reporting from Geneva, said the government delegation and opposition spoke for less than 30 minutes before talks ended on Saturday.

"It was a short, tense session, dominated by differences over how to tackle the issues of violence and political transition," opposition negotiator Ahmad Jakal told the Reuters news agency.

Mounting carnage

A Syrian activist group, meanwhile, said the death toll in Syria's three-year-old civil war has reached 140,000.

The Britain-based Syrian Observatory for Human Rights said on Saturday that the dead include civilians, rebels, members of the military, pro-government militiamen and foreign fighters.

The group bases its count on a network of informants on the ground.

The UN's human-rights office, however, has stopped updating the death toll from Syria's civil war, saying it can no longer verify the sources of information that led to its last count of at least 100,000 last summer.

Source: Al Jazeera and agencies