MEXICO CITY - Mexican federal prosecutors said Thursday they have received complaints that gas stations in the northern border state of Tamaulipas are refusing to fill the tanks of army and police vehicles.

The problem is centred in Nuevo Laredo, across the border from Laredo, Texas. Nuevo Laredo has long been dominated by the old Zetas cartel, which has given birth to a splinter group known as the Northeast Cartel.

The Attorney General’s Office said it is investigating it as a criminal case of refusal of service.

President Andrés Manuel López Obrador was asked Wednesday about reports that the cartel had threatened to attack service stations that sell gas to the armed forces and police. He said the problem was being addressed without punishing the gas stations, but the criminal case announced by prosecutors presumably targets station owners.

Drug cartels in northern Tamaulipas, where Nuevo Laredo is located, have become so bold that they have directly attacked army bases and army patrols. They often wear counterfeit military uniforms, travel in large convoys, use trucks armoured with steel plates and close off streets to traffic.

In some areas of Tamaulipas, drug gangs have mounted their own surveillance systems, including dozens of cameras mounted on light poles, to track the movements of police and military personnel.