A wave of attacks on newspapers and businesses in Monterrey, north Mexico, coincide with reports of a split within the Zetas, which could cause further turmoil in the region.

The Monterrey newspaper El Norte, owned by the national chain Reforma, was attacked on July 29 for the third time in three weeks. In the latest incident, three armed men wearing ski masks arrived in the late afternoon, sprayed gasoline around the office, set it on fire, and fled. The police arrived seconds after the attackers left, but neglected to pursue them. No one was hurt.

A day later, five men attacked a printing press and print media distributor, owned by the company Dipsa. As with the attack on El Norte, the group overpowered the staff, drenched the building with gasoline, and took off after setting it alight. Dispa is the only local magazine and newspaper distributor, making it vital to local publications.

The previous pair of attacks on El Norte occurred a couple of hours apart on July 10, at two different newspaper offices. In each, a group of gunmen targeted the building with assault rifles and grenades. With the most recent incidents, El Norte has now been attacked six times in the past two years.

That time period coincides with a furious battle for dominance in Mexico’s northeast between erstwhile allies the Gulf Cartel and the Zetas. As a result of the split, violence has spiked in Nuevo Leon (where Monterrey is located), Tamaulipas, and Veracruz, among other states. In Nuevo Leon, the number of homicides jumped from 267 in 2009, the year prior to the Gulf-Zetas split, to 2,003 last year, a more than seven-fold rise in just two years. (Interestingly, however, the number of murders in Nuevo Leon this June was half the May total, and scores lower than any other month this year. The July totals have not been released, so it’s not possible to tell whether it was an anomaly or a countervailing trend.) The story is similar in many other areas of northeastern Mexico.

Recent reports of tensions or even an open split between the two principal Zetas bosses, Miguel Angel Treviño and Heriberto Lazcano, threatens to subject northeastern Mexico to a further increase in insecurity. (Mantas denying the split appeared this weekend in three states.) While authorities have not announced which group or specific figure might be responsible for the attacks, a link to the Zetas’ infighting is not implausible. The public’s knowledge of the arguments among the Zetas big shots stems in large part from a series of cryptic messages (known as “narcomantas”) left in a handful of northern cities, Monterrey among them, over the last few months. El Norte was among the first media outlets to report on the mantas, in early June.

Another line of investigation relates to messages left behind at the Dipsa building that was set ablaze. Authorities reported that the assailants painted “S” and “TER” on a wall inside the building, though they have not mentioned what the letters might have been referring to.

Beyond the murder rates, the incidence of large-scale attacks in the region has also spiked in recent years. The Gulf Cartel is thought to have been behind an attack on a Monterrey nightclub in June of 2011 that left dozens dead. The Zetas have been blamed for a notorious attack on Monterrey’s Casino Royale, in which 52 people were killed after the assailants set the building on fire over an unpaid extortion payment.

In Tamaulipas, the state where the Gulf Cartel and the Zetas are historically the strongest, the press have long been targets. In 2006, two gunmen shot up the newsroom of El Mañana, a daily paper in the border town of Nuevo Laredo, wounding one reporter critically. Two years earlier, the same paper’s managing editor was murdered outside of his house.

As the Zetas and the Gulf consolidated their control over new areas, a more aggressive censorship of the press has often followed. In Veracruz, just south of Tamaulipas, reporters covering organized crime have frequently been targets of aggressions, and three journalists were killed there earlier this year. As a result of the attacks, newspapers often resort to self-censorship, either by repeating only the contents of government press releases on crime stories, or by ignoring organized crime-related news altogether.