Some unidentified attackers threw the bomb from their vehicle in front of the main entrance of the el-Qobba palace in Cairo and fled, the official said yesterday.
At least two policemen were severely injured in the explosion.
Police forces and bomb experts rushed to the palace and cordoned off the area in search for other possible bombs and explosives.
The attacks targeting police and military have increased after the ouster of Islamist former president Mohamed Morsi in 2013 and a crackdown was launched on his supporters, leaving more than 1,400 people dead.