At least two inmates were killed in a riot at a prison in Brazil, a media report said.The riot broke out in the Governador Valadares prison of the Minas Gerais state during visiting hours on Saturday morning and ended after a 21-hour standoff, leaving two inmates dead on Sunday, Xinhua reported, citing the local social defence secretariat.During the incident, a group of inmates broke security railings and invaded administration offices to protest the overcrowding of the prison, which, with a capacity for 290 holds some 800 inmates. Police launched an operation to regain control, using tear gas bombs and a helicopter, said the secretariat.Two were killed in the riot, but the cause of the deaths was still unknown, it added.The inmates ended the riot after Judge James Counagno in charge of the prison came to the scene and agreed to analyse their requests.Local media reports said some of the inmates could be distributed to prisons of neighbouring cities.