A second car exploded 45 minutes later outside a police station, also in Ciudad Victoria, where officials are investigating the killing of 72 Central and South American migrants.

Prosecutor missing

The investigation has been complicated, however, by the disappearance of a prosecutor a day after the massacre.

in depth

 

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The Tamaulipas attorney-general's office said Roberto Jaime Suarez disappeared on Wednesday in the town of San Fernando.

Felipe Calderon, Mexico's president, confirmed on Friday that Suarez, a Tamaulipas state prosecutor, was involved in the investigation of the massacre, which authorities have blamed on the Zetas drug cartel.

Reporting on Friday's bomb blast, Mariana Sanchez , Al Jazeera's correspondent in Mexico, said while Televisa has suffered attacks in the past, this one is significant.

"It happened just days after the massacre [of 72 people]. It appears to be a message from the perpetrators, the Zetas, that they are in command here and they don't want any investigating to be done in Tamaulipas state," she said.

Televisa, Mexico's most watched TV network, has had affiliates attacked twice this year, most recently in the northern industrial city of Monterrey two weeks ago.

A van packed with explosives blew up outside a police station on August 5 also in Ciudad Victoria, causing some damage but no injuries.

Escalating drug war

No group was immediately blamed for the August 5 blast but drug cartels set off a car bomb in Mexico's most violent city, Ciudad Juarez, in July, the first of its kind, and another earlier this month in Tamaulipas in Mexico's escalating drug war.

Ciudad Victoria is the capital of Tamaulipas, which borders the US state of Texas.

The Gulf of Mexico drug cartel has been engaged in a bitter turf war with the Zetas drug cartel for control of Tamaulipas' smuggling routes into the US,

More than 28,000 people have been killed in drug-related violence since December 2006, when Calderon launched a nationwide crackdown against narco-traffickers.