A Syrian opposition council, one of the attendees in Riyadh last month, announced on Wednesday it will not join peace talks if a third party joins the negotiations next week.
Riad Hijab, who was chosen by Syrian opposition groups as coordinator of a negotiating body to lead future peace talks, blamed Moscow of blocking negotiations and also said that the opposition could not bargain while Syrians were writhing in consequence of blockades and bombardment.
He also announced the names of opposition figures that would be involved in the negotiating on behalf of the council in any talks.
"The opposition delegation is now ready," said George Sabra, an opposition politician also named as a negotiator.
On Monday, United Nations spokesman Farhan Haq said the Syrian peace talks planned to take place on January 25 may be delayed since the major powers have not reached an agreement on which opposition groups should be invited to the meeting in Geneva, as there is less than a week for the planned date.
The US Secretary of State John Kerry and his Russian counterpart Sergei Lavrov will discuss the meeting on Wednesday.
George Sabra stated that the opposition delegation for the talks is chosen by only the opposition council and countries such as Russia had no right to oppose the opposition team offered.
"No country or side has the right to object to the Syrian (opposition) right to propose whoever they want to represent them and no one has the authority to put forward any names other than the council," he said.
The US, European powers, Turkey and Saudi Arabia back the leaving of Assad from power and support the moderate opposition groups fighting against the regime while Russia and Iran have been strong allies of Assad to whom they provide help, including financial aid and weapons.
The Syrian regime has been laying siege to several towns where thousands of civilians are starving to death, a practice many international figures call a war crime.
According to the UN, more than 250,000 people have been killed since the beginning of the conflict. However, the Syrian Observatory for Human Rights (SOHR) puts the number at more than 350,000.
The war started in Syria in 2001 after peaceful demonstrations demanding freedom and better-living conditions took place.