Forty people, including a child, were killed yesterday when rockets fired by Syrian government forces crashed into a market in a rebel-held area outside Damascus, a monitor said.

The deaths came as top diplomats from 17 countries, including Iran and Saudi Arabia, met for the first time in Vienna to seek a political path out of the conflict.

"There were 40 people killed and at least 100 wounded in the centre of Douma," a town on the eastern edges of the Syrian capital, Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, told AFP.

He added that one child was among the dead.

"There is still heavy fire now, with both rockets and mortars," he said, adding that the toll was expected to rise as people were still being pulled out of damaged buildings.

Rebel-held Douma lies in Eastern Ghouta, the largest opposition stronghold in Damascus province.

A Syrian man carry a wounded after a reported airstrike by Syrian government forces on Douma. Photo: AFP, Reuters

The Douma Coordination Committee, a local activist group, published a gruesome video of what it said was the aftermath of more than a dozen rockets smashing into the market.

Blood-soaked bodies lay crumpled underneath tables of food and other goods, as men gathered around wounded people.

A man mourns a loved at temporary morgue after the strike. Photo: AFP, Reuters

Throughout Syria's brutal war, both the government and opposition forces have been condemned by rights groups for indiscriminate fire on civilian areas.

More than 250,000 people have been killed since the conflict began in March 2011.