Syrian rebels have shot down a helicopter gunship over an area of the northern city of Aleppo, killing at least four people.

The Britain-based Syrian Observatory for Human Rights says the helicopter was shot down with a missile over a poverty-stricken 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 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.