The demonstrators opened fire as the police were breaking through one of numerous barricades put up across the city as the anti-government protests spiralled out of control, a spokesman for the administration said in a statement.
The spokesman said 49 people had sustained minor injuries and several cases of assaults and robberies had been reported, citing hospital and security sources.
"Once again, the government calls on political parties to get their supporters to exercise restraint and urges them to refrain from any form of violence against peaceful citizens," the statement said.