At least 57 people were killed and dozens wounded when Syrian government forces fired missiles into a marketplace in a town near Damascus, a conflict monitor said on Friday.

The Syrian Observatory for Human Rights, which monitors the war through a network of sources on the ground, said government forces fired 12 missiles at Douma, 10 miles (15 km) northeast of Damascus. It earlier said 47 had been killed.

It also said that at least 20 people were killed in the northern city of Aleppo when warplanes struck several parts of the northern city of Aleppo. It was not immediately clear which country carried out the attacks.

Douma has suffered intense bombardment in recent months in a wave of strikes the Syrian army has said targets insurgents that have launched attacks on government-held areas.

Syrian Civil Defence, a local humanitarian rescue group that operates in rebel-held areas, posted a picture on its Facebook page of about a dozen bloodied bodies laid on the ground on plastic sheeting and said more than 45 had died in the attack, which it said used guided missiles.

"Utterly heinous that while world leaders meet for peace in Vienna, attack(s) against civilians continue in Syria," the group said on Twitter.

It linked to a video showing people tending to survivors in a chaotic scene of blackened rubble and fire. Footage showed bodies on the ground of the market place, where stalls had been blown to pieces. Reuters was unable to independently verify the events shown.

Many of Douma's residents have fled the four-year conflict, moving to nearby rural areas. Medics say they have struggled to cope with large numbers of wounded in the intensified strikes.

Syria's civil war has killed more than 250,000 people and driven more than 10 million from their homes. International diplomats were meeting on Friday at a peace conference in Vienna, the first to be attended by President Bashar al-Assad's main ally Iran.

(Reporting by Sylvia Westall, john Davison and Mariam Karouny; Editing by Alison Williams)