BEIRUT — Syria's divided city of Aleppo plunged back into the kind of all-out war not seen in months Thursday, witnesses and health workers said as they reeled from government airstrikes that demolished a hospital in the insurgent-held side and from retaliatory mortar assaults by rebels on the government-held side.
At least 27 people including three children and six staff members were reported killed from the strike on the hospital, which turned it into a smoking pile of rubble Wednesday. At least eight people, mostly civilians, were reported killed from the mortar attacks on government-controlled areas, said officials at a hospital where casualties were streaming in at midday Thursday.
The deadly destruction in Aleppo punctuated a drastic escalation in fighting over the past week that has shattered a partial truce in a war that has consumed Syria for more than five years.
The escalation also threatened to derail renewed attempts at peace talks in Geneva by the United Nations and could disrupt or stop humanitarian aid to besieged parts of the country, affecting millions of people, relief officials said.
"I could not in any way express how high the stakes are for the next hours and days," Jan Egeland, the U.N. special adviser on Syria aid, said Thursday in Geneva as the scope of the destruction in Aleppo became clearer.
Once Syria's commercial center, Aleppo has been an intermittent combat zone for much of the war, split into insurgent and government halves. It had enjoyed somewhat of a respite because of the partial cease-fire — until now.
The scream of jet fighters and thud of shelling could be heard everywhere from Wednesday night into Thursday, residents and aid workers said. Panic and anguish were visible on both sides of the city.
There was no indication that the Syrian government forces of President Bashar Assad and their Russian allies were any closer to retaking the entire city. But it had become apparent in recent days that the truce was unraveling in the surrounding area, with more airstrikes launched by the government and increased shelling by rebels.
More than 100 people, most of them civilians, have been killed, according to tallies by local news media and activists on both sides.
The location of Al Quds hospital, the destroyed facility on the rebel side of the city, was well known, and the hospital was assisted by the international charity Doctors Without Borders.
"This devastating attack has destroyed a vital hospital in Aleppo, and the main referral center for pediatric care in the area," the head of the charity's Syria mission, Muskilda Zancada, said in a statement. "Where is the outrage among those with the power and obligation to stop this carnage?"
Earlier this year in the town of Maarat al-Noaman to the east, two hospitals, including one working with Doctors Without Borders, were hit on the same day, each by multiple strikes. Groups such as Physicians for Human Rights have tracked what they call a pattern of deliberate targeting of health services by government forces.
Witnesses contended that the same appeared to be true in the strike on Al Quds hospital, in the neighborhood of Sukkari.
"Those were multiple airstrikes targeting the same area with less than two-minute gaps," Adnan Hadad, an opposition journalist, said shortly after returning from the scene.
The International Committee of the Red Cross called on all parties to stop indiscriminate attacks and to avoid harming civilians or Aleppo would face what it called a new humanitarian disaster.
"Wherever you are, you hear explosions of mortars, shelling and planes flying over," said Valter Gros, who heads the Red Cross's Aleppo office. "Everyone here fears for their lives and nobody knows what is coming next."
On the government-held side of the city, numerous mortar strikes over the past day mostly hit civilian areas.
Casualties streamed into Al Razi hospital as the wail of ambulance sirens mixed with the thud of explosions in the city streets. Most of the wounded were civilians, including at least three children who were killed, but some were members of the military.
A wounded soldier writhed on the ground, kicking and yelling as a commander comforted him. A man walked down a corridor, carrying limping son. "We will kill them today," he shouted to a reporter.
Hassan Anees, the hospital's executive director, said violence had been rising steadily through the week. Most days the hospital treated at least 20 casualties but on Wednesday the toll reached 39, five of whom died, and by lunchtime on Thursday had reached 54 with eight confirmed dead.
Anees said the rebels appeared to have started using more powerful munitions since the cease-fire crumbled in the city over a week ago.
"First it was mortars, then it was gas canister bombs, and now it is missiles," he said.
As he spoke the rattle of gunfire drifted through his office window, a reminder that the nearest front line was about half a mile from the hospital.
On the insurgent-held side, much of the Quds hospital building had collapsed, and in videos and photographs after the attack, bodies could be seen pinned under rubble and what looked like the metal frames of beds.
A man rushed from the scene carrying the limp body of a small girl in pink clothing, her skin gray with the dust of pulverized concrete. Another girl in pink, her eyes glassy with tears, clung to the shoulder of a man in a red tank top who howled in grief, "Those are my family! I lost my family!"
The hospital was hit when it was already full of victims from government shelling, Hadi Abdullah, an opposition journalist, reported in a video from the scene, in which a medical worker said that three of his colleagues had been killed.
One of them was Mohammad Wassim Mo'az, known by his nickname Abu Abdulrahman, the only pediatrician in the area. A dentist, Ahmad Abulyaman, was also killed.
"I'm crying," Louay Barakat, a journalist and photographer, said by phone after visiting the scene. "My baby's doctor died. About 11 nurses and hospital staff died. Most of them are my friends."
The hospital was the main referral center for pediatrics, with eight doctors, 28 nurses, an emergency room, intensive care unit and operating room, all now destroyed.
In another area, a small boy was captured on video crying over the body of his brother, calling him "the love of my father."
Stroking his body, he said, "I wish it was me, not you."