Violent clashes at two Brazilian prisons have killed at least 18 inmates.<br /><br /> Both incidents are said to be gang-related.<br /><br /> Rondonia<br /><br /> Reports suggest prisoners died of smoke inhalation after mattresses were set alight in the facility in Porto Velho, in the north west of the country. <br /><br /> An official in Rondonia state said the incident was provoked by the transfer to the jail of the leader of a criminal gang. The prison is controlled by a rival gang.<br /><br /> Roraima<br /><br /> It comes a day after clashes between two rival factions killed at least 10 inmates at a jail in Roraima state, in northern Brazil. Among the victims, seven were beheaded and six burned to death, authorities say.<br />
