BEIRUT -- Doctors and nurses at a pediatric hospital in eastern Aleppo scrambled Friday to evacuate babies in incubators to safety from underground shelters after the facility in the besieged Syrian city was bombed for the second time this week.

Medics and aid workers also reported a suspected attack involving toxic gas in a district on the western edge of the rebel-held area. At least 12 people, including children, were treated for breathing difficulties, said Adham Sahloul of the Syrian American Medical Society, which supports health facilities in Aleppo.

Claims of toxic gas attacks are common in Syria, and reports by international inspectors have held the government responsible for using chemicals in attacks on civilians, which Damascus denies.

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Airstrikes also hit a village in rural areas Aleppo province, killing seven members of a family, including four children, opposition activists said.

Friday was the fourth day of renewed assaults by Syrian warplanes on eastern Aleppo districts, a rebel-held enclave of 275,000 people. The onslaught began Tuesday, when Syria’s ally Russia announced its own offensive on the northern rebel-controlled Idlib province and Homs province in central Syria.

Since then, more than 100 people have been killed across northern Syria.

Friday’s airstrikes in Aleppo hit a complex of four hospitals that had been attacked two days earlier. The latest strikes forced the pediatric hospital and a neighboring facility to stop operating.

“Now it is being bombed. ... I am sorry. ... I have to go to transfer the children,” the head of the pediatric hospital wrote in a text message to The Associated Press. The doctor identified himself only by his first name of Hatem because he fears for reprisals against his family.

The incubators already had been moved underground for safety, but with bombs falling all around the facility, hospital workers had to rush them to a safer place despite the danger.

Hatem rushed 14 babies in incubators to another facility a 10-minute drive away while airstrikes continued, he said in a later message.

“As we drove out with the ambulance, warplanes were firing and artillery were shelling,” he wrote. “But thank God we were not hurt.”

Some of the survivors of the suspected gas attack were taken to the children’s hospital.

The cameras of Al-Jazeera, which was broadcasting from the facility as the airstrikes occurred, went dark for a moment. When video resumed, dust was swirling and debris was strewn in the corridors.

Nurses scurried to get babies to safety, and one was seen carrying a blanket-wrapped infant. She then hugged and comforted another nurse who was sobbing as she picked up a baby.

Another hospital in a different Aleppo neighborhood was bombed Thursday night, the doctor told AP. The entrance was set on fire but no one was hurt.

Only four of seven hospitals are still operating in the district, Sahloul said.

The Britain-based Syrian Observatory for Human Rights said dozens of airstrikes, artillery and barrel bombs hit 18 different neighborhoods of eastern Aleppo.

Government bombings have targeted neighborhoods with medical facilities, including the children’s hospital and a nearby clinic that has one of the few remaining intensive care units in eastern Aleppo, the Observatory said.

Many hospitals and clinics in the besieged area have moved their operations underground after months of relentless bombardment. The World Health Organization said that in 2016, it recorded 126 attacks on health facilities, a common tactic over the five years of Syria’s civil war. Russia and the Syrian government deny targeting hospitals.

The city of Aleppo, once Syria’s commercial hub, has been divided since 2012, with the eastern half in rebel hands and the western half controlled by government forces.

Ibrahim al-Haj, a member of the Syria Civil Defense rescue unit in Aleppo, said the city “is a mess.” The group of rescuers and first responders said they are struggling to put out fires set off by the bombings in at least 10 areas.

The Observatory said at least four people were killed in the city’s districts.

It also said the strike that killed the seven family members took place in southwestern Aleppo province. Syrian Civil Defense posted photos showing the bodies of children covered with dust and blood.