The aircraft exploded shortly after touching down, leaving two officers stuck inside the burning wreckage.

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Police battle drug gangs in Rio streets

After the crash, a new gunbattle ensued between the gangs and over 100 policemen, who were backed by Special Police Operations  Battalion (BOPE) troops and an armoured vehicle.

The helicopter had been carrying six police officers as part of an operation in Morro dos Macacos, one of Rio's hundreds of slums, which is dominated by heavily armed drug gangs, police said.

Urban violence is widespread in Rio, where nearly one-third of the two-million-strong population lives in favelas.

Rio's win to host the 2016 Olympic Games, the first ever to be  held in South America, is a serious challenge for the city in terms  of security.

Some 6,000 people were murdered here in 2008 alone.