WASHINGTON - A fight between rival gangs inside a prison in northern Mexico left 31 inmates dead in the latest violence to erupt inside the country's overcrowded jails, local officials said on Wednesday. Clashes between prisoners wielding knives and homemade weapons started around mid-day and were controlled several hours later in Altamira, Tamaulipas, on Mexico's Gulf coast, said state government spokesman Guillermo Martinez. Thirteen other inmates were wounded, the state government said.