Syria crisis: Both sides say Geneva peace talks deadlocked
Talks in Geneva on bringing peace to Syria appear to have reached stalemate with the two sides trading accusations.
Opposition spokesman Louay Safi said the talks had reached an "impasse".
Syrian Deputy Foreign Minister Faisal Mekdad accused the rebel delegation of coming with an "unrealistic agenda".
Violence in Syria continued with reports of a car bomb killing at least 32 people at a mosque in the southern village of Yadouda.
Ten of those killed were children and dozens more people were injured, according to the UK-based Syrian Observatory for Human Rights.
State media confirmed the attack, but put the number of casualties much lower. Witnesses were quoted as saying the blast happened as worshippers were leaving the building.
The Geneva talks, now in their second round, have been going on for five days but delegations representing the government of Bashar al-Assad and the opposition appear far apart.
The Syrian government insists on the need to fight what it calls "terrorists", while the opposition stresses the need for a transitional administration to run the country until elections.
For the opposition, Mr Louay said the government team had failed to show "any responsiveness".
"The regime says something and does something else because it does not have the political will, the will to bring about democracy, responsibility before the people and peace".
The government insists there is no question of replacing President Bashar al-Assad.
"I deeply regret to say that this round did not achieve any progress," Mr Mekdad said.
The UN mediator, Lakhdar Brahimi, is planning to bring the two sides together again for a face-to-face meeting on Saturday, starting at 11:00 (10:00 GMT).
He has said US and Russian officials have assured him that they will try to "unblock the situation".
The United Nations has meanwhile warned of a large military build-up near the rebel-held town of Yabroud near the border with Lebanon.
"According to reports we have received from within Syria, there have been numerous aerial attacks and shelling, along with a military build-up around the town suggesting a major assault by land may be imminent," said UN human rights spokesman Rupert Colville.
Up to 50,000 civilians were estimated to remain in the town, he said, with thousands having fled over the past few days.
Syrian government forces were reported on Thursday to have resumed their artillery and aerial bombardment of the town, the last rebel stronghold in the Qalamoun mountains - a region the regime considers strategically important.
The UN refugee agency says it is preparing for an influx of refugees out of Yabroud across the border into Lebanon.
The evacuation of civilians from the besieged Old City of Homs has paused, according to the UN.
The UN's local aid chief Yacoub el Hillo told the BBC the idea was to "review our plans and prepare for the next phase" focusing on the most vulnerable groups such as the elderly and disabled.
The evacuation over the past few days was agreed under a UN-brokered ceasefire between the warring parties.
The UN says 1,400 people have been evacuated, but 381 men and boys aged between 15 and 55 remain in Syrian government detention.
There are concerns about the fate of those detained as the government seeks to weed out those men it considers rebel fighters.
Earlier, UN humanitarian chief Valerie Amos urged the UN Security Council to act immediately to ensure more humanitarian access in Syria.
The Security Council has been deadlocked over aid deliveries in Syria, where millions have been forced to flee their homes.
Speaking to the BBC's Nick Bryant, Baroness Amos said the ceasefire deal which has allowed civilians to be evacuated from Homs did not offer a long-term solution.
"If it's going to take 14 months to do that when you've got 250,000 people in besieged communities, when you've got over three million people in hard-to-reach communities, I really find it very difficult to say that this is a [right] model."
The civil conflict in Syria has claimed more than 100,000 lives since March 2011. Some 9.5 million people have been forced to flee their homes.