Maputo - The mayor of Mozambique's third city was shot dead outside his house by unknown gunmen, officials said Thursday, in an apparent targeted assassination.Mahamudo Amurane, mayor of Nampula, was killed on Wednesday evening, sparking angry demonstrations in the northwestern city, where he was widely seen as an anti-corruption crusader."He was murdered by a man who shot him three times as he left his private residence," Saide Ali, a member of the Nampula municipal government, told reporters.On Thursday police fired warning shots in Nampula to control angry crowds who gathered to protest against his death and to call for justice."The Nampula City mayor had bravely tackled corruption head on," Amnesty International said in a statement."It is no secret that this made him a target of attacks, even within his own Mozambique Democratic Movement (MDM) party."It added that Amurane had tried "to root out corruption in the city's administration and revitalise public infrastructure."Amurane was elected mayor in 2013 representing MDM, Mozambique's third-largest party, but last year said he was leaving the party and would run in next year's elections as an independent.Daviz Simango, the MDM leader, described the killing as a "brutal and senseless crime"."Unfortunately we have seen other past and recent murders that hang like shadows in our society without being solved," Simango said.The US embassy described the killing as a "detestable act" and called for a thorough investigation.Last year, a public prosecutor who pursued a wave of kidnapping cases was shot dead outside his house in Beira city by unknown men.And in 2015 a French-Mozambican lawyer who was critic of the government was gunned down while leaving a cafe in the capital Maputo.