The main Syrian opposition coalition has urged the United Nations to pause peace talks until Damascus "shows it is serious about political transition" as rebel groups vowed to strike back against alleged truce violations.
Staffan de Mistura, the United Nations mediator, said on Monday that the coalition delegation would stay in Geneva, but postpone its formal participation in the negotiations.
They are pausing the talks "in order to express their own displeasure and concern on the humanitarian situation degradation and on the problems related to the cessation of hostilities," said de Mistura.
"Their intention is to remain in Geneva in their hotel and possibly at my own suggestion to pursue technical discussions with myself and my team."
De Mistura said the talks still had time as the timetable for getting a new constitution and getting a political transition was up to August.
"We should not expect, and no one should expect, that after five years of a conflict a political transition by miracle in one week is solved," he said.
Riad Hijab, the head of the coalition, said that it was "unacceptable" for the talks to carried on while President Bashar al-Assad's forces continued to "bombard and starve civilians" in Syria.
Hijab said that the Syrian government and its allies have used the talks as a "pretext" for waging their military campaign. He says the government has also kept up its siege of civilian areas.
READ MORE: Syria rebels declare new offensive on government
In February, the United States and Russian-brokered cease-fire brought weeks of relative calm to much of Syria, but appears to be breaking down across the north, where rebels have launched an offensive they say is in retaliation for government breaches.
Both sides have repeatedly accused the other of violating the truce.
The Syrian Observatory for Human Rights said 22 civilians were killed on both sides over the weekend in divided Aleppo city - one of the highest single tolls since the truce began.
"This was the bloodiest incident in Aleppo and its province" since the ceasefire started, Observatory head Rami Abdel Rahman said. "This escalation directly threatens the truce."
State television reported another eight people killed on Monday by rebel rocket fire into regime-held areas.
On Monday, a statement by 10 rebel groups announced the end of truce.
"After the increase of violations by regime forces that included targeting displaced people and continuous bombing of residential neighbourhoods, we declare the start of the battle in response," said the statement.