An airstrike and artillery fire hit the two largest hospitals in rebel-held parts of Syria's Aleppo on Wednesday, September 28, in what rights groups said was a deliberate strategy of targeting civilian infrastructure, AFP reports.

President Bashar al-Assad's forces and his ally Moscow have carried out a barrage of air strikes on opposition-controlled eastern Aleppo since Syria's regime announced a bid last week to retake all of the divided city.

Dozens of civilians have been killed, residential buildings have been reduced to rubble and residents of eastern districts -- already suffering under a government siege -- are facing severe shortages of food and medical supplies.

The latest bombardment of the city has been some of the worst in Syria's five-year civil war, and comes after the failure of a short-lived ceasefire brokered by Russia and the United States earlier this month.

The two hospitals were struck just before dawn, with the M10 facility hit in an air strike and the M2 facility hit with artillery fire, said Adham Sahloul of the Syrian American Medical Society (SAMS), which supports both hospitals.

The attacks put both facilities temporarily out of commission and left only six hospitals operational in the eastern parts of the city, Sahloul said, calling the attacks "deliberate".

It was unclear who had carried out the bombings, AFP says.

"I am in the M2 hospital now. I was inside when the entrance to the emergency room was hit. Three of my colleagues were hurt," said Aref al-Aref, a medical assistant trapped inside.

"Everyone is terrified and scared today. We are afraid that we will be today's victims," he told AFP.