Foreign ministers of global and Middle Eastern powers should meet to salvage the shaky truce in Syria and the stumbling peace talks in Geneva, UN Syria envoy Staffan de Mistura said Friday in Geneva.
The United States and Russia had brokered a ceasefire in February through their respective alliances with Syrian opposition rebels and the regime, but the opposition walked out of the Geneva talks this week to protest the re-escalation of the conflict.
The truce was still in effect, de Mistura said, "but it is in great trouble if we don't act quickly."
As the truce and the humanitarian efforts that have supported the peace talks were in danger, "it is time to call the International Syria Support Group," he said, referring to the group of countries that has influence on Syria's conflict parties, and that is led by Washington and Moscow.
Although the opposition has formally suspended its participation in Geneva, de Mistura said he had continued informal but "very, very productive" talks with some delegates who stayed behind, as well as with the government side.
The UN peace broker said he planned to continue the current round likely until Wednesday, in order to work towards a political transition in Syria.
While the opposition seeks a transitional government without President Bashar al-Assad, the government still has not made it clear what it means when it says it wants a "broad-based government," according to de Mistura.
"Is this going to be cosmetic, is it going to be real? And if it is real, what does it mean for the opposition?" de Mistura said.
The UN envoy spoke on the end of a day of escalating violence on the ground in Syria.
Air raids which targeted rebel-held areas in the northern city of Aleppo killed 19 people, the Britain-based Syrian Observatory for Human Rights reported.
"Today has been the worst day in Syria for over a year," the humanitarian group White Helmets, which operates in rebel areas, said on its Twitter feed.
US President Barack Obama admitted this week while visiting Saudi Arabia that the ceasefire was "under tremendous strain," and he placed much of the blame on al-Assad.
NATO Secretary General Jens Stoltenberg noted that Russia maintains a considerable military presence in support of al-Assad's regime.
George Sabra, a member of the opposition delegation, which has largely withdrawn from Geneva, said the airstrikes in Aleppo showed that the decision to pull out of the talks was correct.
"The ceasefire is dead," he told dpa by telephone.
However, de Mistura maintained that none of the sides had officially renounced the truce.
Activists this week were especially alarmed by an airstrike on a market in Maarat al-Numan, in rebel-held Idlib province, which killed about 50 people.
Aleppo remains a key point of concern. Control of the pre-war economic hub is divided between rebels and government forces and militias loyal al-Assad.
There is concern the government plans to impose a siege on the rebel-held sections of the city, where tens of thousands of people live.
"Regime and Russian planes conducted the raids on several rebel-held residential areas," Mahhmoud Shahabi, an activist in Aleppo city told dpa, referring to the raids that killed 19 people.