A Syrian government airstrike hit a vegetable market in the northern city of Aleppo on Saturday, killing at least 21 people, activists said.
For nearly two weeks, President Bashar Assad's warplanes and helicopters have pounded opposition-controlled areas of the divided city. Activists said the aerial assault has killed more than 400 people since it began on December 15.
The campaign comes in the run-up to an international peace conference scheduled to start January 22 in Switzerland to try to find a political solution to Syria's civil war.
The Observatory, which relies on a network of activists on the ground, said 25 people, including four children, were killed and dozens were wounded in the strike. The Aleppo Media Centre published a list of 21 names of people it said were killed in the air raid.
An activist with the Aleppo Media Centre, Hassoun Abu Faisal, said the airstrike took place around 10am local time.
"Cars were damaged, debris and rubble are everywhere," he said.
Both Abu Faisal and the Observatory reported airstrikes in other opposition-held areas of Aleppo, including Myassar, although there was no immediate word on casualties.
Aleppo, Syria's largest city, has been a major front in the country's civil war since rebels launched an offensive there in mid-2012. The city has been heavily damaged since then in fighting that has left it divided into rebel- and government-controlled areas.