A wave of airstrikes and shelling killed more than 60 people in less than 24 hours in the northern Syrian city of Aleppo, monitors and activists said Thursday. The contested city is now one of the main battlegrounds of Syria’s devastating civil war, with a cease-fire that has collapsed and peace talks in Geneva stalled.

At least 27 people died as a hospital supported by Doctors Without Borders and the International Committee for the Red Cross and nearby buildings were hit overnight in the rebel-held part of Aleppo.

The U.N. envoy for Syria appealed early Thursday on the United States and Russia to help revive the peace talks and a cease-fire, which he said “hangs by a thread.”

However, the violence only escalated. New airstrikes Thursday in residential areas in the rebel-held part of the city killed at least 20 while state media reported that at least 1,000 mortars and rockets were fired at government-held areas of Aleppo, killing at least 14 civilians.

The chief Syrian opposition negotiator Mohammed Alloush blamed the government of President Bashar Assad for the violence. He told The Associated Press that it shows “the environment is not conducive to any political action.” He denounced the intensive bombing as an attempt by Assad’s government to drive the residents of Aleppo out, labelling it “a crime of ethnic and sectarian cleansing.”

About 200 civilians have been killed in the past week in Syria, nearly half of them around Aleppo. There has also been shelling in Damascus, along with a car bombing — both rarities for the capital. The ICRC said the fighting, including the destruction in airstrikes overnight of a key hospital in Aleppo, is putting millions at grave risk.

With peace talks in Geneva completely deadlocked, Syrians are regarding the escalating bloodshed with dread, fearing that Aleppo is likely to be the focus of the next, more vicious, phase of the war.

Rebel commanders said government forces have been mobilizing soldiers, equipment and ammunition in preparation for a military action in Aleppo.

The well-known al-Quds filed hospital supported by MSF and ICRC and located in the rebel-held district of Sukkari was hit shortly before midnight Wednesday, according to opposition activists and rescue workers. Six hospital staff and three children were among the 27 who died there.

The hospital has been one of the main medical centers operating in Aleppo since the city became deeply divided in 2012.

Dating back to the 1990s, the hospital was renamed after the area came under rebel control to carry the name of one of the uprising’s early victims, Basel Aslan, who was detained and tortured to death, said civil defense volunteer Ibrahim Alhaj. It received aid and assistance from various foreign groups, as well as a volunteer medic from the United States, according to its Facebook page.

The Syrian Civil Defense, a volunteer first-responders agency whose members went to the scene of the attack, put the death toll at 30 and said the dead included six hospital staff. Among those slain was one of the last pediatricians remaining in opposition-held areas of Aleppo and a dentist.

The defense agency, also known as the White Helmets, said the hospital and adjacent buildings were struck in four consecutive airstrikes. It said there were still victims buried under the rubble and that the rescue work continued. The Britain-based Syrian Observatory for Human Rights said three children were among the 27 victims but it was not immediately clear if they were patients at the hospital.

MSF said in a statement that at least 14 patients and staff were among those killed, with the toll expected to rise, and that the hospital was “hit by direct airstrike.” It was the area’s main pediatric care center.

“Where is the outrage among those with the power and obligation to stop this carnage,” asked Muskilda Zancada, MSF head of Syria mission.

The 34-bed, multi-story hospital had an emergency room and offered services such as obstetric care, outpatient and inpatient treatment. It had an intensive care unit and an operating theatre. Eight doctors and 28 nurses worked full time in the hospital, the MSF said, adding it has supported the hospital since 2012.

An unnamed Syrian military official quoted on state TV denied reports that the hospital was targeting, saying they were false.

A video posted online by the White Helmets showed a number of lifeless bodies, including those of children, being pulled out from a building and loaded into ambulances amid screaming and wailing. It also showed distraught rescue workers trying to keep onlookers away from the scene, apparently fearing more airstrikes.

Shortly after midday, new airstrikes in rebel-held areas killed at least 20 people in two neighborhoods, the Syrian Civil Defense and the Observatory said.

Videos provided by activists show scenes of dust rising up from buildings on fire as men and women run away from collapsing houses and children cry, looking for their parents. In one clip, a man is seen lifting his daughter out of the rubble.

State media said at least 1,300 rockets and missiles fell Thursday in residential areas in government-controlled parts of the city, killing 14 people.

Alloush, one of the leading opposition negotiators in the Geneva talks, described the airstrikes as one of the latest “war crimes” of Assad’s government.

“Whoever carries out these massacres needs a war tribunal and a court of justice to be tried for his crimes. He does not need a negotiating table,” Alloush told the AP in a telephone interview. “Now, the environment is not conducive for any political action.”

Syrian lawmaker Omar Ossi, who was part of the government delegation in Geneva talks, blamed the escalation on Turkey and Saudi Arabia as patrons of the rebels. “The Syrian army will be able to regain initiative and rein in this Turkish interference,” he said.

The end-of-February cease-fire has been fraying in recent weeks as casualty figures mount, particularly in Aleppo and across northern Syria. Airstrikes earlier this week also targeted a training center for the Syrian Civil Defense, killing five volunteers in rural Aleppo.

Since April 19, nearly 200 people have died, including at least 44 in an airstrike on a market place in rebel-held area in northern Idlib province, as well as dozens of civilians in government-held areas from rebel shelling.

U.N. envoy Staffan de Mistura told the Security Council via videoconference that after 60 days, the cessation of hostilities agreed to by both sides “hangs by a thread.”

“I really fear that the erosion of the cessation is unraveling the fragile consensus around a political solution, carefully built over the last year,” de Mistura said in his briefing. “Now I see parties reverting to the language of a military solution or military option. We must ensure that they do not see that as a solution or an option.”

The talks foundered last week after the main opposition group, called the High Negotiating Committee, suspended its formal participation to protest alleged government cease-fire violations, a drop in humanitarian aid deliveries and no progress in winning the release of detainees in Syria.

(AP)