At least three children are among more than 27 dead after an air strike hit a hospital in the Syrian city of Aleppo.

The bombing was part of new wave to hit rebel-held areas of the city. At least 30 more civilians have been killed by the strikes, which local sources said were either carried out by Russian or Assad government's war planes. The Syrian military has said it did not target the hospital. 

Violence has escalated in Syria in recent days and on Monday Christian and Kurdish neighbourhoods in Aleppo were attacked. At least eight children died in the fighting in the district of Sulaymaniyah.

Over the past six days as violence has increased, government air strikes have killed 91 civilians in rebel held areas and 49 have been killed by rebel shelling in government held areas, according to the British-based Syrian Observatory for Human Rights (SOHR).

Aleppo is on the brink of a humanitarian disaster, the International Committee of the Red Cross (ICRC) has said from Geneva.

"Wherever you are, you hear explosions of mortars, shelling and planes flying over," said Valter Gros in a statement.

"There is no neighbourhood of the city that hasn't been hit. People are living on the edge. Everyone here fears for their lives and nobody knows what is coming next."

The increasing violence helped to undermine UN-led peace talks in recent weeks. A cessation of hostilities agreement has unravelled and fighting has resumed on numerous fronts in western Syria.

The hospital was supported by the charity Medecins sans Frontieres (MSF). One local activist told the BBC buildings around the hospital were also hit.

"It was an air strike by two rockets, heavy rockets from a Russian air strike," he said.

"Near the hospital one building on five floors just crumbled and just crashed down and we don't know how many dead will be under these ruins."

An MSF spokesman told the BBC that Aleppo's last remaining paediatrician had been killed in the strike.

He said: "He kept it going, was always there and always worried about the needs of the people. He was honest and very committed. He worked in conditions you cannot even begin to imagine."

The Syrian state media has made no mention of the attack but said 14 had been killed on Thursday by rebel shelling in government held areas.

More than 270,000 have been in Syria's ongoing civil war which has torn the country apart since 2011. Millions have been forced to flee.

Additional reporting by Reuters.