The UN special envoy for Syria says the government delegation has not yet confirmed that it will attend the latest round of UN-mediated talks with the opposition in Geneva.
The eighth round of Geneva talks is supposed to focus on the issue of elections and a constitution, two of the four so-called baskets of reforms laid out by the UN for a political settlement to the Syria crisis.
"The government did not yet confirm its participation in Geneva but indicated that we would be hearing from them soon," Staffan De Mistura said.
"Naturally we hope and indeed expect that the government will be on its way shortly."
De Mistura said there was a real danger of the "concrete fragmentation" of Syria, and that he was ready to engage with all those who came to the talks.
Al Jazeera's James Bays, reporting from Geneva, said that the talks in the Swiss city, due to begin on Tuesday, were "probably" not going to start on time.
"The opposition are already here," he said.
"The Syrian government delegates have postponed their flight to Geneva because they are angry that the opposition still say that [Syrian President] Bashar al-Assad must go."
Syria's opposition groups agreed last week, following a meeting in Riyadh, Saudi Arabia, to send a united delegation to Geneva, a move seen as a boost to prospects for a breakthrough.
However, our correspondent said there are some who believe there is another reason why the government delegation has delayed its arrival.
"It's also been suggested that maybe they want to continue the bombardment on Eastern Ghouta for a little longer before they come to the negotiating table, potentially with a strengthened hand," he said.
During a summit meeting with Russian President Vladimir Putin in the Black Sea resort of Sochi last Monday, al-Assad said he was "ready for dialogue with all those who want to come up with a political settlement."
More than 330,000 people have been killed in Syria's six-year war, and over half of its population has been displaced.
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