The explosives rigged vehicle exploded in the middle of the afternoon in Ciudad Victoria, shattering police station windows, said an official from the state prosecutor's office in Tamaulipas.

"It was a car bomb and two people were injured," said the official, who declined to be identified.

Four children who had been in the playground were unhurt, he added.

The country's first car bombing occurred in July in Ciudad Juarez, Mexico's most violent city, and there have been several others since then.

It was not immediately clear who was responsible for the latest attack.But Tamaulipas, which borders Texas, has seen a surge in violence in recent

years amid a turf war between the Gulf drug gang and its former allies the Zetas.

On Tuesday the military confiscated 5.1 tons of marijuana from an abandoned warehouse during a routine patrol elsewhere in the state.

More than 34,600 people have been killed in drug-related violence in Mexico since 2006, when President Felipe Calderon launched a military crackdown against the country's powerful drug cartels.

But violence has continued to grow unchecked in parts of Mexico despite the deployment of tens of thousands of troops.