powerful blast shattered the façade of a security headquarters in downtown Cairo before dawn Friday morning.

The explosion, which the interior ministry said killed at least three people, sent showers of glass across several nearby blocks in the heart of the city, and tore metal doors of shops and shutters off their hinges, some half a kilometer away.

Hundreds of people gathered at the attack site within an hour of the explosion, some of them chanting “the people want the execution of the Muslim Brotherhood!”

Riot police on the scene moved to push angry spectators away from the damaged building as ambulances and fire engines pushed through the crowds. Two foreign journalists reported being chased by civilian mobs.

The nearby Islamic Museum, housed in a colonial-era building, was also damaged in the blast “