Thousands of angry anti-government demonstrators took to the streets Friday in several Egyptian cities and clashed with police who fired tear gas to quell the crowds. In Cairo, the capital, vans packed with riot police circled neighbourhoods before the start of weekly prayers Friday afternoon. But protesters, fed up with high unemployment and a lack of freedoms, defied security warnings to demand an end to President Hosni Mubarak's authoritarian 30-year-rule. Protesters hurled rocks and chanted that Mubarak, the dictator, must go. The Muslim Brotherhood -- Egypt's largest opposition bloc -- urged its followers to protest after prayers, the first time in the latest wave of unrest that the group has made such a call.