In a separate incident, gunmen also killed a police commander and his family, including four children. They opened fire on the man's house as the family slept, then pummeled it with grenades, setting it on fire.

The latest killings come amid a fierce government crackdown on major drug traffickers. President Felipe Calderon has launched tens of thousands of troops throughout the country, but the violence continues to surge.

In Ciudad Juarez, an especially volatile city across Mexico's northern border from El Paso, federal investigator Jose Ibarra was shot to death late Tuesday as he arrived home from work, the attorney general's office said.

Ibarra was the lead detective investigating the November 2008 slaying of Armando Rodriguez, a well-respected veteran crime reporter for the city's El Diario newspaper, the largest daily on the border. Rodriguez, who covered local bursts of the drug war, was shot to death in front of his home. Authorities said they were investigating whether the two killings were connected.

Also Wednesday, police in Acapulco announced the discovery of the body of another journalist, Juan Daniel Martinez Gil, who had been badly beaten and buried alive, his head wrapped in plastic. Martinez worked for two radio stations but was not known to cover drug trafficking.

Mexico is one of the most dangerous places in the world for journalists. At least 27 have been killed in Mexico since 2000, according to the New York-based Committee to Protect Journalists. The organization recently reported that state investigators had identified drug cartel members as suspects in Rodriguez's killing, but that federal officials had not acted on the information.

The death of police commander Jesus Romero and his family occurred before dawn Wednesday in the Gulf of Mexico port city of Veracruz. Investigators told reporters that Romero and his wife apparently died of multiple gunshot wounds, and the children -- the youngest 7, the eldest 15 -- died of smoke inhalation.

More than 11,000 people have been killed in Mexico's drug-related violence in the last 2 1/2 years, most of them traffickers or law-enforcement agents. It is rare for an entire family to be targeted.

In the western state of Michoacan, meanwhile, government troops pressed ahead in a major offensive against one of the newest and most violent cartels, known as La Familia. Six suspected members of the group were arrested, authorities said Wednesday, including a woman believed to be the girlfriend of purported drug boss Servando Gomez Martinez and La Familia's alleged chief financial operator, Armando Quintero Guerra. Authorities said Quintero Guerra also managed La Familia's contacts with associates in Los Angeles.

wilkinson@latimes.com