Gunmen have opened fire on a minibus filled with plainclothes police in a Cairo suburb, killing eight of them, including an officer.

Egyptian state media said the police were inspecting security in the south Cairo neighbourhood of Helwan early on Sunday when four gunmen in a pick-up opened fire.

Insurgents have carried out a wave of attacks, mainly targeting Egyptian security forces, since the military overthrow of Islamist president Mohammed Morsi in 2013.

The attacks have been concentrated in the Sinai Peninsula, where an Islamic State affiliate is based, but militants have also struck the mainland, including in the capital.