Eyewitnesses and police say party rivals of Egypt's most prominent jailed dissent Ayman Nour stormed his party's headquarters and set it on fire, injuring seven people, the Associated Press reported.
The violence was the latest infighting in the opposition al-Ghad party, bitterly divided between Nour supporters and those of a pro-government leader.
Eyewitness Hussein Amin said about 200 protesters first pelted the al-Ghad headquarters in downtown Cairo with stones and bottles. Then they used aerosol cans to spray flames at the offices, located in an old building that also houses two 19th century restaurants and shops.
Later, the official Middle East News Agency reported that Cairo prosecutors questioned Nour's wife, Gamila Ismail and 37 other people who took part in the incident.