Security officials say rioters have stormed a Muslim Brotherhood headquarters building in northern Egypt, and a teenager protester was killed.
It was the first death in three days of street battles after a power grab by the country's president.
A 15-year-old died and 40 people were injured in the clash between protesters and police late Sunday in the town of Damanhoor in the Nile delta, according to security officials. They spoke on condition of anonymity because they were not authorized to brief reporters.
The demonstrators are protesting Egyptian President Mohammed Morsi's decree granting himself immunity from judicial review as well as other measures neutralizing the judges.
Egypt's stock market plummeted nearly 10 percent on Sunday, the first day of trading since Morsi's assumption of extra powers.