A former prison official, who resigned recently after a bar was found at the facility where he worked, was gunned down outside his house in Chihuahua city, the capital of the like-named northern Mexican state, prosecutors said.

Fernando Oropeza, former deputy warden at the minimum-security prison in Chihuahua city, was killed by several armed men on Wednesday in the state capital's Dale neighborhood.

Oropeza, a retired army infantry captain, resigned on May 25 in the wake of the discovery by the Federal Police of a makeshift bar at the prison, where liquor, knives, firearms, billiard tables, drugs and nearly 500 banned appliances were seized.

Oropeza alleged on Monday that the bar and banned items were "planted" by Chihuahua state prison bureau chief Luis Alfredo Franco to incriminate him.

The former prison official said Franco was seeking revenge because he had reported him to the army for corruption and extortion.

Oropeza filed a complaint last Thursday with the Chihuahua State Human Rights Commission, or CEDH, which opened an investigation into the death threats he had received.

CEDH director Jose Luis Armendariz said last Friday that officials at Chihuahua city's minimum-security prison refused to allow him to enter the facility, a decision that he called "suspicious" and "a serious irregularity."

An inmate at the minimum-security prison was murdered a few minutes after Oropeza's killing, but it is not known whether the two crimes were related.

"An operation is being coordinated with different police agencies to quickly and transparently clear up" Oropeza's murder, the Chihuahua state Attorney General's Office said.

Chihuahua, considered Mexico's most violent state, is home to Ciudad Juarez, a border city across the Rio Grande from El Paso, Texas, where more than 900 people have been murdered this year.

The violence in Ciudad Juarez is blamed on a brutal war for control of the border city being waged by the Juarez and Sinaloa cartels with backing from hit men from local street gangs.