Syria's opposition on Monday urged the UN to pause peace talks until Damascus shows it is serious about political transition, as rebel groups vowed to strike back against alleged ceasefire violations.
With fighting surging around Syria's second city of Aleppo and negotiations in Geneva stalled over the fate of President Bashar al-Assad, the opposition High Negotiations Committee said it would ask UN mediator Staffan de Mistura to put the talks on hold.
"A small delegation has come to meet (de Mistura) and to ask him to pause the negotiations until the regime shows it is serious about political transition and humanitarian issues," an HNC member told AFP.
Speaking on condition of anonymity, he said the delegation planned to remain in Geneva, for now.
Three HNC delegates entered a meeting with de Mistura at 3:00 pm (1300 GMT), with the UN envoy expected to address the media afterwards.
- 'Start of the battle' -
HNC coordinator Riad Hijab said earlier it was "unacceptable" for the negotiations to continue while Assad's regime continues to "bombard and starve civilians" in Syria.
The ceasefire agreed in February dramatically curtailed violence across much of Syria, but the fresh fighting around Aleppo has prompted tens of thousands of people to flee.
"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 a statement by 10 rebel groups.
The landmark ceasefire agreed between the United States and Russia took effect on February 27, raising hopes that a lasting deal could be struck to end Syria's five-year civil war.
But the spread of fighting around Aleppo and the regime's apparent unwillingness to hold concrete talks on forming a new government has led the opposition to question Assad's commitment to a political solution to a conflict that has killed more than 270,000 people.
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.
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Among the armed groups that signed Monday's statement was Jaish al-Islam, the most important opposition faction in East Ghouta, a key rebel-held town east of Damascus.
Mohammed Alloush, the HNC's chief negotiator in Geneva and a senior member of Jaish al-Islam, on Sunday urged rebel groups to "strike" regime positions.
"Don't trust the regime and don't wait for their pity," he wrote on Twitter. "Strike them everywhere."
A fellow opposition figure said this did not represent the HNC's position and Alloush clarified that he was calling on rebels to defend themselves from attacks.
- New ideas? -
Syria's UN ambassador Bashar al-Jaafari, the regime's lead negotiator in Geneva, on Monday referred to Alloush's comments as "irresponsible and provocative".
He also denounced Israel for holding a cabinet meeting on Sunday in the occupied Golan Heights.
Without elaborating, Jaafari referred to ideas "raised for the first time" in the government delegation's meeting with de Mistura on Monday.
The peace plan outlined by de Mistura and backed by world powers envisions a political transition, a new constitution, and presidential and parliamentary elections by September 2017.
Alloush also repeated that there could be "no compromise" on Assad's removal -- which the regime has called a "red line".
He also said a rebel offensive had already begun in northern Lattakia province, Assad's heartland.
Areas in Syria controlled by the Islamic State (IS) group, Al-Qaeda's local affiliate Al-Nusra Front, and other jihadists are exempt from the ceasefire, but renewed Aleppo clashes are straining the truce as other rebel groups are dragged into the fighting.
IS has seized fresh territory from rebel groups in the north, threatening the key opposition town of Azaz, just eight kilometres (five miles) south of the Turkish border.
The jihadist onslaught has forced 30,000 Syrians to flee, and tens of thousands more are at risk of displacement.
In addition to Jaish al-Islam, the rebel statement was signed by the powerful Islamist Ahrar al-Sham faction, which is allied to Al-Nusra and fights alongside it around Aleppo and in neighbouring Idlib province.