Syrian government aircraft have dropped barrel bombs on the contested northern city of Aleppo, killing at least 22 people, including 14 children, activists said.

Aleppo has been a major front in the Syrian civil war since rebels launched an offensive on the city in mid-2012. Nearly a year and a half of fighting has destroyed much of the city, while also cutting it up into rebel-held and government-controlled areas.

Government helicopters pounded the neighborhoods of Haidariya, Ard al-Hamra and Sukhour with barrel bombs filled with explosives, the Britain-based Syrian Observatory for Human Rights said. Observatory director Rami Abdurrahman said Syrian air force jets were also flying sorties over the same districts.

An amateur video posted online showed the aftermath of one strike on Sukhour. A crowd gathered in a narrow street littered with shattered masonry and other rubble from a house that appeared to have been hit by the airstrike.

The Observatory, which monitors the conflict through a network of activists on the ground, also said the number of people killed in the town of Adra north east of Damascus after an al Qaida-linked rebel faction attacked on Wednesday has risen to 32.

Mr Abdurrahman said the dead are primarily members of the Alawite sect, as well as a few Druse and Shiite Muslims.

The killings point at the dark sectarian overtones the conflict has taken on since the uprising against President Bashar Assad began with largely peaceful protests in March 2011.

Assad is an Alawite, and members of the offshoot of Shiite Islam form the core of his security forces. Other minorities in the country, including Christians, Druse and Shiites, have mostly sided with Assad or remained on the fence, fearing a takeover of the country by Islamic extremists. The rebels, meanwhile, are primarily Sunni Muslims.

The Observatory and Syria's SANA state news agency both reported fighting in Adra today.