A top Syrian official has urged the opposition to let go of its "dream" of forcing President Bashar Assad out of power, a key demand by the opposition in peace talks in Geneva.

Deputy Foreign Minister Faisal Mekdad told the Associated Press that a transitional government amounts to a coup d'etat and will never be accepted.

"We have to proceed then we need to forget or we need others to forget the dreams they had for the last five years and to come with factual actual solutions to the problem including what we said about the possibility of establishing a national unity government or a broad government.

The situation we find with the so-called opposition is that there are five, six groups which, I mean, makes it impossible to negotiate a viable agreement. Unless these groups are united and this is the main responsibility of the special envoy Mr de Mistura we cannot reach such an agreement. We cannot sit, I mean, together," he said.