Security officials say rioters have stormed a Muslim Brotherhood headquarters building in northern Egypt, and a teenage protester was killed.

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. It was the first death in three days of street battles.

Egypt's stock market plummeted nearly 10 percent on Sunday, the first day of trading since Morsi's assumption of extra powers.

A spokesman for Egyptian President Morsi said on Sunday, however, that the president was committed to engaging "all political forces" to reach common ground on the constitution and stressed the "temporary nature" of a decree expanding Morsi's powers.

"This declaration is deemed necessary in order to hold accountable those responsible for the corruption as well as other crimes during the previous regime and the transitional period," the spokesman said in a statement.

Facing a storm of protest from judges and political opponents who accuse Morsi of turning into a new dictator, the president's spokesman said the decree was "not meant to concentrate powers," but to devolve them. It aimed to avoid the politicization of the judiciary, the statement said.

It also aimed to "abort any attempt" to dissolve either the body writing Egypt's constitution or the upper house of parliament, both dominated by Islamists allied to Morsi, the statement added.

"The presidency stresses its firm commitment to engage all political forces in the inclusive democratic dialogue to reach a common ground and bridge the gap in order to reach a national consensus on the constitution," it added.