The UN Syria mediator said on Monday that the main opposition would no longer attend talks at the United Nations in Geneva in protest against the worsening situation on the ground, but said it would remain in the Swiss city for informal discussions.
Staffan de Mistura said that the gap between the High Negotiations Committee (HNC) and that of the Syrian regime remained "clearly wide" although both sides were talking about political transition.
"On Friday we will take stock of the discussions, review what we have come up with, having learned from every side their own positions, and then decide on how and when how to move forward on what is expected anyway to be a series of discussions on and off in order to focus on political transition," de Mistura said.
The opposition's coordinator at the Geneva talks, Riad Hijab, said earlier it was unacceptable for talks to go on if the regime and its allies pushed on with sieges and bombing civilian areas.
"We asked for the postponement of talks, only a postponement until the conditions are right," Mohammad al Aboud, a member of the negotiating team said.
The HNC later confirmed the decision in a statement, saying a pause would be "a chance ... to respond to the core subject of forming a governing body that has no role for Assad."
The HNC emphasised that it was not walking out of the talks, the first attempt to negotiate a way out of the five-year-old conflict in two years; a diplomat said they wanted the UN to publicly criticise the regime.
Syrian opposition declares 'battle' against regime
Syrian opposition groups called for a new “battle” against regime forces on Monday after Assad's forces violated the cessation of hostilities deal in the country, which went into effect on February 27.
Syrian regime forces killed at least five civilians on Monday right after they had killed 22 others in Aleppo on Sunday.
The groups, which are fighting under the banner of the Free Syrian Army and Ahrar al Sham, confirmed in a statement that they would respond "with force" against any army group that fired on civilians.
The opposition chief negotiator, Asaad Al Zoubi, said there could be "no compromise" on Bashar Assad being removed from power, and called for renewed attacks on regime forces.
"I'm sure you are asking, what are the latest developments from the negotiations. We are not going to keep negotiating indefinitely; we have given a time limit to the regime, to De Mistura and to all the nations who claim to be our friends or our enemies," Zoubi said.
Zoubi also called the opposition fighters to retaliate to regime’s assaults.
"We are upset with the rebels inside Syria; we have never asked them to be silent against any harm caused to them by the regime. If the regime targets them with one missile, they must respond with ten, and they must gain control of as many areas as possible, they must take advantage of the ceasefire as the regime has done," he said.
Humanitarian situation is deteriorating
The Syrian Observatory for Human Rights (SOHR) said the number of civilians killed in Aleppo city was one of since the cessation deal took effect on February 27.
SOHR said that the deal has seen the violence drop across parts of Syria, including the northern city, but renewed clashes, in the past 24 hours, have seriously strained the cessation of hostilities.
At least six civilians were killed and eight others wounded in regime air strikes on opposition-held eastern parts of the city on Saturday.
Opposition groups fired rockets at western areas of Aleppo city late Sunday, but there was no immediate information on new casualties.
"The humanitarian situation is continually deteriorating, the issue of the detainees has not seen any progress, the ceasefire has almost collapsed, and now there is an attack on Aleppo from three sides," Abdulhakim Bashar said in Switzerland.
"Given these factors, we are reviewing everything, and we will continue our meetings today [Sunday] so that tomorrow we can decide what to do."
More than 300,000 people have been killed in the six-year-old conflict and more than 10 million displaced.
A rival opposition group Ahrar al Sham launched a scathing attack on the opposition negotiators and the peace process, saying the outcome "so far was negative and it had provided free political gains for the regime."
Fighting near Aleppo has been escalating for two weeks, mostly to the south of the city where regime forces backed by Lebanon's Hezbollah and other militias have been waging fierce battles with militants including the Nusra Front.