Two children were among at least 18 people killed in new air strikes on a rebel-held district of Syria's main northern city of Aleppo on Tuesday, a watchdog said.

It was the third straight day of air raids on the city, Syria's commercial hub before a rebel offensive in July last year made it a key battleground in the conflict that erupted in March 2011, the Syrian Observatory for Human Rights said.

A woman was also among the dead, which killed 15 people in the Shaar district and three in Maadi, the Britain-based watchdog said.

The raids follow air strikes on rebel-held areas of Aleppo Sunday and Monday that killed 86 people, including 32 children.

The air force has been dropping barrels of explosives in a bombing campaign using both helicopters and fixed-wing aircraft, activists and the Observatory say.

A security official said the military prefers the TNT-packed barrels because they are cheaper than regular bombs, which need to be imported from Russia.

Observatory director Rami Abdel Rahman said there was a "marked escalation" in attacks, and that "this type of intensive bombing over several days demonstrates the desire of the army to advance" on rebel-held areas.

He said the focus of the bombing has been on eastern districts of Aleppo neighbouring regime-held areas. In the past two months, loyalists forces have captured numerous cities and towns to the east of Aleppo.

Turkey says 'no war weapons' sent to Syria
Istanbul (AFP) Dec 17, 2013 - Turkey's defence minister on Tuesday denied reports that his country was delivering weapons of war to Syrian rebels, but acknowledged that "hunting rifles" had been exported to Syria.

"No war weapons have been exported to Syria in 2013," Ismet Yilmaz said in parliament, according to media reports.

Hurriyet Daily News reported on Monday that Turkey had shipped 47 tonnes of weapons to Syrian rebels since June, citing UN and Turkish Statistics Institute documents.

Turkey is a fierce opponent of Syrian President Bashar al-Assad and has openly supported the rebels, but has always denied arming them.

Yilmaz said his ministry had not issued any permits for the export of military equipment to Syria in 2013.

"However, what has been exported are ungrooved hunting rifles and blank firing guns. Other than that, any export by us is out of question," Yilmaz was quoted as saying.

A powerful Islamist faction seized weapons warehouses on the Turkish border from the Western-backed Free Syrian Army earlier this month, highlighting concerns that Syria's moderate opposition may be in disarray.

The United States and Britain responded by suspending all non-lethal aid to the FSA.

Turkey, which has been accused of turning a blind eye to fighters crossing its border into Syria, is sheltering about 600,000 Syrian refugees who have fled the civil war as well as the main Syrian opposition group.