Syrian government air strikes killed at least six civilians, including a baby, in a rebel-held town outside the capital Damascus on Thursday, a monitor and local medics said.

The strikes hit the town of Douma, which lies in the Eastern Ghouta region, where a "de-escalation zone" deal agreed by regime allies Iran and Russia and rebel backer Turkey has been in place since July.

At a medical facility, an AFP photographer saw the bodies of at least two people killed in the strikes, as well as adults and children being treated for their wounds by harried medical staff.

Despite the truce deal, there has been an uptick in government bombardment on Eastern Ghouta in recent days.

Humanitarian groups have also warned of a malnutrition crisis in the area, which is under a tight government siege.

"Regime planes fired rockets on several parts of Douma," said Rami Abdel Rahman, director of the Syrian Observatory for Human Rights, a Britain-based monitor.

"Six civilians were killed, including a child," he said, adding that 21 others were wounded.

At the medical facility, two bodies were lying on beds, each covered in a bright yellow sheet.

Medics worked to treat the wounded, including 13-year-old Ziad, who suffered a head injury after being caught up in the strike on his way home.

"I was coming back from school when the first strike hit and I hid in a doorway," he told AFP, sitting with his head bandaged and blood still coating the bridge of his nose.

"The plane came back a second time and I tried to get down to the basement, but the force of the second strike knocked the door closed and it injured my head and nose."

Behind him, a younger boy cried in terror, rubbing at his eyes with both his hands.

- Blockade and malnourishment -

Men lay on beds or stretchers, some shirtless and already being bandaged, others waiting to be treated and covered in blood.

Five children, the youngest just a toddler, sat wide-eyed on a bench as medical staff tended to the wounded.

Up to 400,000 people are believed to live in Eastern Ghouta, which has been under government siege since 2013.

The blockade has caused serious food and medicine shortages, and pushed the prices for what remains beyond the reach of impoverished residents.

At least two children are reported to have died from malnourishment or related complications in recent weeks, and more than 1,100 other children are reportedly suffering acute malnutrition.

On Monday, several dozen trucks carrying assistance for 40,000 people entered Eastern Ghouta as part of a United Nations-Syrian Arab Red Crescent convoy.

It was the first aid access since September, despite repeated requests from the UN and humanitarian actors for consistent access to besieged areas like Eastern Ghouta.

On Tuesday, 11 people including six school children were killed in regime shelling on the town of Jisreen in Eastern Ghouta, the Observatory said.

More than 330,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests.