Activists say Syrian rebels have shot down a helicopter gunship over a slum in the northern city of Aleppo, killing at least four people.

According to the Associated Press, the Britain-based Syrian Observatory for Human Rights said the helicopter was shot down with a missile over a poor area of town known as Camp Nairab.

Helicopters are used by President Bashar Assad's forces to drop barrel bombs — crude explosives that have killed thousands of people and caused widespread destruction, especially in Aleppo. Rebels have rarely succeeded in downing helicopters.

The Observatory and an Aleppo-based activist who goes by the name Abu Saeed Izzedine said the crash killed four people, including a child.

Aleppo, once Syria's commercial capital, has seen heavy fighting since rebels seized part of the city in 2012.