One policeman was killed and 15 others were injured on Saturday after a motorcycle rigged with an explosive device went off near a police training centre in the Egyptian Nile Delta city of Tanta, state television reported.
Four of the injured are in critical condition, according to the report.
Earlier Saturday, the Interior Ministry said that 16 people, including 13 policemen and three civilians, were injured in the blast.
An obscure group, calling itself the Brigade of the Revolution, claimed responsibility for the attack.
The online claim could not be independently verified.
Authorities had previously linked the group to the now-outlawed Muslim Brotherhood.
Egypt has seen a series of attacks mainly against security forces since the army's 2013 overthrow of Islamist president Mohammed Morsi, a senior Brotherhood official, following mass protests against his rule.
Most attacks have taken place in the Sinai Peninsula that borders the Palestinian Gaza Strip and Israel.
A group loyal to the Islamic State radical militia has taken credit for several of these attacks.
