The protest movement sweeping Iran spread to a Tehran prison known as a symbol of political repression in a new challenge to the Islamic Republic, with detained dissidents chanting antigovernment slogans before violence erupted and a deadly fire engulfed the facility, activists said. Authorities said the fire killed four inmates and blamed a planned escape attempt on Saturday for the mayhem at Evin Prison, a complex in north Tehran erected by the shah five decades ago that serves as a political prison for dissidents and foreigners . A large fire was visible at Evin from the densely populated neighboring communities, and loud bangs were heard through much of the night.