The fighting in Mansoura, in the Nile Delta, followed calls on Sunday for a campaign of civil disobedience to protest President Mohamed Morsi and the Muslim Brotherhood, al-Ahram reported Wednesday.
The headquarters of the Daqahliya governorate was attacked and part of the building set on fire Wednesday evening during a protest over the state prosecutor's decision to hold for four days those arrested in earlier clashes with the police.
Confrontations Tuesday between anti-Muslim Brotherhood demonstrators and police left dozens injured and arrested.
The attack Wednesday night destroyed the air conditioning unit, furniture and documents in a second-story office, al-Masry al-Youm said.
Demonstrators in Mansoura also blocked streets and set tires on fire.