Two car bombs exploded in northern Mexico early on Friday, days after marines found the bodies of 72 people gunned down in the country's escalating war with powerful drug cartels.

The blasts, the second and third modest-sized bombs planted in a vehicle this month in Ciudad Victoria, the capital of the northern Gulf state of Tamaulipas, and the fourth in Mexico since late July, caused no casualties but damaged buildings.

The attacks came the same day officials discovered the body of a police officer investigating the massacre of dozens of migrants in the latest attack linked to Mexico's drug war.

I'm told of the explosion of two car bombs here in the state, one in the offices of local traffic police and the other in the installations of Televisa, Tamaulipas Governor Eugenio Hernandez told local radio, referring to Mexico's top broadcaster.

The explosion on the street outside Televisa's studios in Ciudad Victoria, located 220 miles (350 kms) south of the Texas border, apparently part of a growing campaign of intimidation of the media, left little more than the car's engine and front chassis.

Televisa did not give details of the blast, and it was unclear what explosives were used or how the two bombs were detonated. No group was immediately blamed for the explosion.

Car bombs are a new weapon in Mexico's drug war. So far, the devices appear to have been relatively unsophisticated and have not caused widespread destruction.

Four people were killed in July in the violent city of Ciudad Juarez by a bomb planted in a car, the first such attack since President Felipe Calderon took office.

More than 28,000 people have died in drug violence since Calderon launched his war on drugs in late 2006.

Fourteen drug-related slayings were reported on Friday in different locations in the Pacific beach resort of Acapulco, popular with U.S. tourists but also a key transit point for narcotics. Several of the bound and blindfolded victims were covered with messages threatening rival cartels.

MEDIA IN CROSS-HAIRS

As gruesome attacks become more common, Calderon is seeking to convince civic leaders, businessmen and opposition politicians his war is making headway.

The paradox is that in other areas there can be advances ... in improving the economy, in social policy, but while this matter keeps weighing heavily on the daily life of ordinary people the country will not move forward as much as it should with its enormous potential, Calderon said at a security forum in Mexico City.

The explosion at Televisa was at least the fourth apparent attack on its studios in northern Mexico since last year, when drug hitmen threw a grenade at its studios in Mexico's business capital, Monterrey. Grenades were also thrown at Televisa in Monterrey and Matamoros across from Brownsville, Texas, earlier this month, police said. No one was hurt in the attacks.

They want to sow terror in society and they are going for symbols. Televisa has a big presence at a local level in this region, said Alberto Islas, an independent security analyst with crisis management firm Risk Evaluation. The attack is not against the company but against freedom of expression.

At least 30 journalists have been killed in Mexico since 2006, according to Mexican media. The country is among the world's most dangerous for reporters, the U.S.-based Committee to Protect Journalists says.

INVESTIGATOR KILLED

Tamaulipas state has become one of Mexico's bloodiest drug flashpoints since the start of the year as rival hitmen from the Gulf cartel and its former armed wing, the Zetas, fight over smuggling routes into the United States.

Gunmen murdered a popular candidate for state governor in June in Mexico's worst political killing in 16 years.

The car bombs come after the bodies of 72 people were found on Tuesday at a ranch about 100 miles (160 km) from Ciudad Victoria, the worst massacre since Calderon sent 45,000 troops and thousands of federal police to fight cartels in late 2006.

The victims, believed to be trying to make their way into the United States from Central and South America, appeared to have been blindfolded and bound before being shot. A military source in Tamaulipas said the Zetas were behind the killings.

Two senior police officers who were investigating the massacre were abducted on Thursday and the body of one of them was dumped on a rural road on Friday, El Universal daily said.

(Reporting by Reuters newsroom in Ciudad Victoria; additional reporting by Miguel Angel Gutierrez and Cyntia Barrera in Mexico City; Writing by Robin Emmott and Robert Campbell; editing by Todd Eastham)

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