Mexico’s Justice Department has opened an investigation into a Sunday night grenade attack on the Vanguardia newspaper, in the northern city of Saltillo.

The explosion did not cause any injuries, but damaged the newspaper’s building and some cars parked in front. The Vaguardia attack seems to be an attempt to scare the newspaper’s editorial staff, something that has become increasingly common in the region.

Saltillo, which lies about half an hour west of Monterrey in the border state of Coahuila, was the site of the murder of Valentin Valdes, a reporter for the local daily Zocalo, in January 2010. Over the past two years, there have been seven attacks on media outlets in Coahuila; over the past five years, the figure comes to 22.

Coahuila is considered to be territory of the Zetas drug gang, who were suspected of the murder of Valdes. The once-peaceful state, which has a number of small border crossings as well as key transit routes to Monterrey and larger border towns like Nuevo Laredo and Reynosa, has turned more violent in recent years as the Zetas have battled it out with the Sinaloa and Gulf Cartels.