The policemen were either in or close to their car when the device went off in or near a garbage can, the sources said, Reuters reported.
The attack, close to a government building in a middle class neighborhood of Cairo, was the latest in a series of security incidents in Egypt often claimed by extremists.
There was no immediate claim of responsibility for the attack in Al Haram street leading to the Pyramids, in which four civilians were also hurt.
Ansar Bayt al-Maqdis (ABM), formerly known as “The Sinai Province,” is currently the most active group staging terrorist operations in Egypt. It is affiliated to the Takfiri Daesh terrorist group.
Militants from the group have carried out numerous attacks on security forces and judiciary officials since the ouster of the democratically-elected president Mohamed Morsi in 2013.
Most of the group’s attacks have been focused on targets in the restive Sinai Peninsula; however, deadly bombings have also been staged by the Sinai Takfiris in Cairo and some other Egyptian cities.
In June 2015, the Takfiris killed Egypt’s top state prosecutor, Hisham Barakat, in a car bomb attack.