"I met the delegations of the opposition and the government separately yesterday (Thursday) and again today (Friday) and tomorrow (Saturday) we expect, we have agreed, that we will meet in the same room," Brahimi told journalists.
Pulled together by the UN, Russia and the US, delegations from President Bashar al-Assad's regime and the opposition had been due to sit down early today at UN headquarters in Geneva for their first face-to-face talks.
But Brahimi was unable to convince them to sit together, after the opposition insisted the regime must be prepared to discuss Assad leaving power.
The regime has threatened to withdraw from the talks should "serious sessions" fail to take place tomorrow, but Brahimi appeared confident no one would be immediately walking away from the talks.
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"Both parties are going to be here tomorrow and they will be meeting. Nobody will be leaving on Saturday and nobody will be leaving on Sunday," he said, stressing that the sides had "absolutely" agreed to talk face-to-face.
"We hope that it will be a good beginning and that we will continue until the end of next week," he said, adding that at some point the parties would likely take a break from the discussions for a few days before continuing.
"We have not discussed the core matters yet. We hope that both parties will give concessions that will be to the benefit of the process," he said.
He said both sides had agreed that the negotiations would be based on an agreement reached at the "Geneva I" peace conference in 2012, but acknowledged that there were "some differences on the interpretation of some of its items" of the document.
"Among the many things we hope to be able to achieve is to clarify the ambiguity on those points," he said.
The opposition arrived in Switzerland with a sole aim -- toppling Assad -- while the regime says any talk of removing the Syrian leader is a "red line" it will not cross.