Gunmen have killed three policemen and injured five others in a shooting in the Egyptian capital, Cairo.

The gunmen fired on a security convoy and police returned fire.

While no one has claimed responsibility for the attack, Egypt has been fighting an insurgency by a local affiliate of the so-called Islamic State group in North Sinai province.

Hundreds of soldiers and policemen have been killed in the insurgency since the army overthrew Islamist president Mohammed Mursi in 2013.

Following deadly church bombings last month, President Abdel Fattah al-Sisi declared a three-month state of emergency on 10 April.

The so-called Islamic State group said it was behind the church bombings in Tanta and Alexandria on 9 April that killed 45 people.

The military has killed several of the group's top leaders, but the extremists have increasingly expanded their attacks from Sinai to other parts of Egypt, including Cairo.