An explosion in Port Said has rocked the headquarters of the city's Workers' Union Federation, Egypt's state broadcaster reported.
No casualties or injuries were reported in the incident on Tuesday morning.
The explosion caused damage to the building's outer wall and to the windows and windshields of nearby cars, the broadcaster reported.
Another explosion took place close to a police station on Tuesday in Egypt's second city Alexandria.
Police said it killed the person was on his way to plant the device, as well as injuring two others, also in the car where the bomb was being transported.
Militants have targeted police and army facilities and personnel, killing hundreds of them in attacks since the ouster of Islamist president Mohamed Morsi in 2013.
Over 200 militants have been killed by Egyptian security forces so far, according to the latest official figures.
Dozens of bombs were defused on Sunday, the fourth anniversary of Egypt's 2011 revolution, police said.