The United Nations special envoy for Syria, Steffan de Mistura, says the Syrian government has not yet confirmed its participation in the next round of peace talks in Geneva this week.
"Last night, we received a message that the government would not travel to Geneva today. Naturally we hope, and indeed expect the government will be on its way shortly," de Mistura told the UN Security Council on November 27.
The latest round of UN-sponsored talks aimed at finding a political solution to Syria's six-year civil war -- the eighth since 2012 -- is due to start in the Swiss city on November 28.
De Mistura said it would focus on getting to an "inclusive process" to draft and ratify a new constitution.
He also said he would "not accept any preconditions by any party" to the negotiations.
After arriving in Geneva on November 27, the head of the opposition delegation, Nasr Hariri, said that the group was aiming for the removal of President Bashar al-Assad.
The pro-government newspaper Al-Watan earlier reported that the Damascus delegation would delay its arrival in Geneva because of the opposition's insistence Assad step down.
The opposition has accused the government of refusing to seriously engage.
More than 330,000 people have been killed in Syria and millions have been driven from their homes since the conflict began in March 2011 with a crackdown on antigovernment protests.
Russia supports Assad's government and provides air support for government forces. Iran also backs Assad, while the United States and Turkey support differing rebel groups.
Russian President Vladimir Putin repeated his call for a negotiated political settlement to end the conflict during a surprise visit by Assad in Russia's Black Sea resort city of Sochi on November 20.
Expressing thanks for Russia's role in the Syrian conflict, Assad said, "especially since we've attained victory over the terrorists, we want the political process to progress."
Talks sponsored by Russia, Iran, and Turkey are being held in the Kazakh capital, Astana, to deal with battlefield issues, such as cease-fires and the creation of "de-escalation zones." The zones have led to reduced violence in many areas, although deadly air strikes have continued.
Russia, Iran, and Turkey have also proposed holding a "national congress" of government and opposing forces in the Russian city of Sochi, although no date has been set.