JOIN USThe initial toll was eight, but a ninth person died overnight, a spokesman for the state Public Safety Office said.
All state and federal security forces were put on alert at 7 p.m. Wednesday after shots were heard from inside the prison in Durango city, the state capital, according to a statement from the Public Safety Office.
The battle at the prison follows the discovery since early last month of 218 bodies buried in clandestine graves at various locations in the city.
Media accounts suggest those deaths are related to turf wars among rival drug cartels.
In a meeting two days ago, President Felipe Calderon promised Durango Gov. Jorge Herrera Caldera "all the support necessary" in the "struggle for security".
The president also vowed to press "the investigations aimed at bringing to justice those responsible for the deaths of people found recently in clandestine graves".