CIUDAD VICTORIA, Mexico (June 29, 2012)--An explosion in a pickup truck wounded seven people outside city hall in the border city of Nuevo Laredo, authorities said.

The grenade went off around 11:15 a.m. Thursday in the truck parked outside the main municipal building of the city across the border from Laredo.

The seven victims were hospitalized with non-life-threatening injuries, a statement from local officials said.

The facade of the city building was damaged, along with nearby cars.

Nuevo Laredo and the surrounding state of Tamaulipas have been the scene of brutal battles between the Zetas cartel and its former ally, the Gulf cartel, which is now allied with the Zetas' biggest rival, the Sinaloa cartel led by Joaquin "El Chapo" Guzman.