At least four people including three police officers were killed in an hours-long prison shootout involving inmates and security forces in a northern Mexican border state. <br/><br/>State security spokesman, Alberto Rodriguez said three state police officers and one unidentified person were killed and six others were wounded in the incident at the lockup in Ciudad Victoria, the capital of Tamaulipas state. <br/><br/>Police said the inmates were armed with automatic rifles.Relatives of prisoners said the violence apparently broke out due to a conflict between local inmates and others who were recently transferred from a prison in the border city of Nuevo Laredo. <br/><br/>Uprisings are relatively common at Mexican prisons, where inmates are often in de facto control of their own environments.