A wave of Syrian air strikes on Sunday killed at least 19 civilians and wounded dozens across the besieged rebel enclave of Eastern Ghouta near Damascus, a monitor said.

The deadliest raids hit the town of Hammourieh, killing 13 civilians including five children, the Britain-based Syrian Observatory for Human Rights said.

Other air strikes on the towns of Arbeen, Beit Sawa and Misraba killed six civilians, among them two children and two women.

The Observatory said the death toll was likely to rise given the critical wounds suffered by dozens of people.

In Hammourieh, an AFP photographer saw men carrying the body of a victim wrapped in a blue blanket across a rubble-littered street, a shoeless foot sticking out.

The strikes appeared to hit a modest residential neighbourhood, smashing a small convenience store and caking a vegetable stand in a layer of dust.

Victims were taken to a nearby clinic where doctors could be seen treating a man wincing from a gash above his knee.

In another room, the lifeless soot-covered body of a boy lay in a pool of blood.

Eastern Ghouta, one of the last remaining rebel strongholds in Syria, has been under a heavy government siege since 2013 that has caused drastic food and medical shortages.

An estimated 400,000 people still live in the enclave, and the United Nations has warned that hundreds are at risk of death if they are not evacuated for urgent medical treatment.

The area is one of four "de-escalation zones" aiming to curb violence across war-ravaged Syria, agreed earlier this year by regime allies Russia and Iran and rebel backer Turkey.

Syria's government agreed last week to a ceasefire in the region to coincide with the resumption of UN-led peace talks in Geneva.

But heavy bombardment of the opposition enclave near the capital has resumed, with another 11 civilians killed on Saturday.

More than 340,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests.