At least 70 people were killed and 550 injured after airstrikes and shelling hit a marketplace on the outskirts of Syria's capital Damascus, according to the medical aid organization Doctors Without Borders, which quoted medics on the scene as saying the wounds from the attack were "worse than anything they have seen before."

The attack occurred on Friday in the city of Douma, east of Damascus, and was reportedly carried out by Syrian government forces loyal to President Bashar al-Assad.

Doctors Without Borders (also known as Médecins Sans Frontières or MSF) released a statement on Saturday that said rescue teams came under additional shelling as they tried to attend to the wounded after the initial airstrike.

Graphic footage from the aftermath of the bombing showed rescuers attempting to pull the dead and severely wounded from piles of debris and rubble.

"This was an extremely violent bombing," said the director of an MSF-supported hospital in the area. "The wounds were worse than anything we've seen before, and there were large numbers of dead. We had to do many amputations… We did our best to cope, but the number of critically wounded was far beyond what we could handle with our limited means."

MSF noted that bombing of civilian infrastructure such as hospitals and markets has increased in the areas around Damascus in recent weeks. In Douma, medical workers struggled to treat the influx of casualties from the latest airstrike because the nearest makeshift hospital had been bombed the previous day.

The medical aid group voiced fears that the bombing seen in northern and central Syria in October "could become even more horrific if it spreads to besieged areas around Damascus, where almost one million people are trapped with no way to escape and few medical facilities, and no options for medical evacuations of the seriously wounded."

Nearly 40 percent of people treated in MSF-supported facilities in East Ghouta, an agricultural area in the Damascus countryside, have been women and children under 15 years old, the group said.

"This massive bombing on a crowded market and the repeated destruction of the few available medical facilities breaches everything that the rules of war stand for," said Brice de le Vingne, director of Syria Operations for MSF.