UN mediator for Syrian peace talks Lakhdar Brahimi is to hold separate talks with rival delegations to assess their willingness to meet together, BBC News reports.

The behind-the-scenes negotiations follow the first day of a major peace conference in Switzerland which ended in bitter divisions.

Brahimi's initiative takes place before full talks resume on Friday, Jan 24.

It remains unclear whether the two sides will negotiate face-to-face - as planned by the UN - when talks restart. Brahimi has revealed that he still does not know if the two sides are even prepared to sit in the same room. He intends to consult them separately on Thursday to gauge what is possible, the BBC says.

"What we will try to do is talk about how to end this bloody war, and for that, I think, we have a kind of road map in the communique of June 30, 2012, and we'll see how we use that platform to best effect," Brahimi said. "We have no illusion that it is going to be easy, but we are going to try very hard."

At a fractious news conference late on Wednesday, during which there were repeated calls for calm, UN Secretary General Ban Ki-moon spoke of the suffering in Syria, saying: "Enough is enough. The time has come to negotiate."

He said that "the really hard work begins on Friday", adding: "We have a difficult road ahead, but it can be done and it must be done. We did not expect instant breakthroughs. No-one underestimated the difficulties."

U.S. Secretary of State John Kerry said: "There is no way - no way possible in the imagination - that the man who has led the brutal response to his own people could regain the legitimacy to govern."

However, earlier on Wednesday Syrian Information Minister Omran al-Zoubi told reporters: "There will be no transfer of power and President Bashar Assad is staying."