BEIRUT -- A Syrian government airstrike hit a crowded vegetable market in a rebel-held neighborhood of the northern city of Aleppo on Saturday, shattering cars and storefronts and 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 say the aerial assault has killed more than 400 people since it began Dec. 15.
The campaign comes in the run-up to an international peace conference scheduled to start Jan. 22 in Switzerland to try to find a political solution to Syria's civil war. Some observers say the Aleppo assault fits into Mr. Assad's apparent strategy of trying to expose the opposition's weakness to strengthen his own hand ahead of the negotiations.
Saturday's airstrike slammed into a marketplace in the Tariq al-Bab neighborhood, the Aleppo Media Center activist group and the Britain-based Syrian Observatory for Human Rights said.
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 Center published a list of 21 names of people it said were killed in the air raid.
The discrepancy could not be immediate reconciled, but differing death tolls are common in the chaotic aftermath of such attacks.
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.
Another critical battleground is around the capital, Damascus. Mr. Assad's forces have a tight grip on the heart of the city, but many of the suburbs have been opposition strongholds since the early days of the uprising.
In a grueling campaign that has lasted months, government forces have managed to capture some of the rebel-held towns and villages ringing Damascus, while others have held out despite daily shelling and months-long sieges.
One such town is Moadamiyeh, which activists say has been strangled by a government siege for nearly a year. Mr. Assad's troops have set up checkpoints around the community west of Damascus, and have barred entry to food, clean water and fuel in a bid to pressure residents to expel rebels from the town.
The blockade has had a devastating effect on those stuck inside. For months, activists in Moadamiyeh have warned that malnutrition is rife among the town's estimated 8,000 civilians. Last week, residents reached a deal with the army that would see the town receive food in exchange for raising the government flag over Moadamiyeh. The agreement also demanded rebels hand over their heavy weapons and that only registered residents may remain in the town.
Locals hoisted the flag above Moadamiyeh Thursday. Late Saturday afternoon, three small pickup trucks entered with bread, rice and canned food, said Moadamiyeh-based activist Qusai Zakarya.
"It's very, very small shipment. We have over 8,000 civilians. They have brought in around three tons of food," he said. "This amount of food won't be enough for 1,000 civilians for one day."
Also Saturday, the U.N.-backed international mission to rid Syria of its chemical weapons confirmed it is unlikely to meet a Dec. 31 deadline to transport the most critical chemical material out of the country.
A statement by the joint mission of the Organization for the Prohibition of Chemical Weapons and the U.N. said that external factors, primarily security concerns, were responsible for the delay.