The UN-Arab League envoy to Syria has said that peace talks between the Syrian government and rebel groups will not go ahead as planned in November.
Lakhdar Brahimi however said on Tuesday that diplomats were "still striving to see if we can have the conference before the end of the year".
The announcement came after he met senior diplomats in the Swiss city of Geneva in a new push to prepare the already long-delayed peace conference. President Bashar al-Assad's government signalled it was not ready to negotiate handing over power.
Brahimi said that the opposition was divided on its aims. "It's no secret for anybody, and they are facing all sorts of problems and they are working very, very hard to get ready. And they are not ready," Brahimi said.
He said that a Russian call on Tuesday that Iran must be invited to negotiations were being considered, but discussions were not complete.
Ahmad Jarba, the president of the opposition Syrian National Coalition, said it would not attend without a clear time frame for Assad's departure, and also opposed Iran being at the talks.
He said Iran's invitation would be a "provocation".
Jarba, who heads the main umbrella opposition emphasised the group's commitment to attending Geneva II only as a united front and reiterated its unequivocal demand for a ceasefire during the talks.
The coalition has said it plans to meet in Istanbul, Turkey, on Saturday to decide whether to attend the peace talks, but the Syrian National Council, a key member of the bloc, has threatened to quit if it does so.
Brahimi has said that "if the opposition does not participate there will be no Geneva conference".
The veteran Algerian diplomat said after a meeting with Assad in Damascus last week that the Syrian government had agreed to take part in the talks while the opposition was "trying to find a way to be represented".