Complicating matters further, the US and Russia clashed over the pace of Syria's handover of chemical arms for destruction, with Washington accusing Damascus of dragging its feet, putting the plan weeks behind schedule, and Moscow - President Bashar al Assad's big-power ally - rejecting this.
US Secretary of State John Kerry said Syrian authorities had no excuse for delays in shipping its poison gas arsenal abroad under a deal reached last year.
Moscow said Mr Assad was acting "in good faith" and that a June 30 deadline for eliminating the chemical agents remained viable.
UN mediator Lakhdar Brahimi, who has tirelessly pursued a peace deal other diplomats consider "mission impossible", said the opposition delegation would be back on February 10, but Mr Assad's delegates had told him they would have to check with Damascus before agreeing to return.
Mr Brahimi said: "They didn't tell me they are thinking of not coming. On the contrary, they said they would come but they needed to check with their capital."
He listed 10 simple points on which he felt the two sides agreed in the talks, and said he thought there was more common ground than the sides recognised.
But neither side has budged an inch from their main positions: the opposition wants the talks to focus on a transitional administration it says will remove Mr Assad from power, while the government wants to talk about fighting "terrorism" - a word it uses to refer to all of its armed foes.
Mr Brahimi said: "Progress is very slow indeed, but the sides have engaged in an acceptable manner."
Syrian Foreign Minister Walid al Moualem blamed the lack of tangible results on what he called the immaturity of the opposition delegation and their "threats to implode" the talks, as well as blatant US interference.
He said there was no pressure on his delegation from Russia, but there was coordination between Damascus and Moscow.
Expectations had always been low for a breakthrough on political issues at the talks, the first between Mr Assad's representatives and his foes in an almost three-year-old conflagration that has killed 130,000 Syrians and driven one-third of the population from their homes.
The sides also failed to achieve more modest aims, such as an agreement to allow aid convoys into Homs, Syria's third largest city, where thousands of civilians are trapped with no access to food or medicine.
Mr Brahimi admitted: "Homs was extensively discussed, although unfortunately there has been no breakthrough yet,"
The Syrian Observatory for Human Rights, a UK-based monitoring group, said 1870 people had been killed during the week of talks, including 450 civilians and 40 who died from inadequate access to food and medicine in areas besieged by government troops.
With few achievements on substance, diplomats say the priority now is just to keep the talks process going in the hope hardline positions can be modified over time.