A bomb on Sunday exploded outside a military intelligence building in northern Egypt, reported state television.
The blast in the town of Inshas left at least four people injured, said state-run newspaper al-Ahram, citing a local police official.
Sixteen people were killed earlier this week when a car bomb hit a police headquarters in the northern city of Mansoura.
The military-backed government blamed the Mansoura attack on the Muslim Brotherhood and labelled it a terrorist group.
Security forces and buildings have been the target of attacks carried out by suspected Islamist insurgents since the army deposed president Mohamed Morsy of the Brotherhood in July.
Hundreds of Brotherhood supporters have since been killed in a security crackdown.