Authorities in Cameroon are investigating a fire inside a maximum-security prison in the port city of Douala that sent three inmates to the hospital with serious burns.A fire official said two firefighters were also injured Thursday trying to put out the blaze at the New Bell jail in the commercial capital.Firefighters were able to keep the fire from spreading to a heavily populated neighborhood close to the prison.It is unclear what started the fire, nor if the fire was linked to overcrowded conditions in the prison.Human rights groups, including Amnesty International, say overcrowding, poor sanitation and violence are chronic issues confronting Cameroon prisons. 
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