The arrest sparked violence in the Mexican border city of Nuevo Laredo

CIUDAD VICTORIA, Mexico — Gunfire erupted in the Mexican border city of Nuevo Laredo early Monday, prompting the cancellation of classes and a shelter-in-place order at the U.S. consulate.

President Andrés Manuel López Obrador said the shootings were in response to the arrest of a cartel leader, but did not elaborate. The city has long been dominated by the Northeast Cartel, which is a descendant of the old Zetas gang.

The US Consulate in Nuevo Laredo has canceled visa appointments for the day.

“There is an emergency in Nuevo Laredo following an arrest operation. Reports of gunfire in several parts of the city. Shelter in place and standby for further information,” the consulate said.

A military officer, who cannot be named, said the suspect was the leader of the Northeast cartel’s notorious “Troops of Hell” killing squad. This squad acts as the cartel’s enforcement arm and is often mixed up with law enforcement and military forces.

The officer identified the detainee as Heriberto Rodríguez Hernández, known by the nickname “Negrolo” or “Negro 35.” Negro means black in Spanish, but it is unclear whether the nickname refers to his race.

Mayor Carmen Lilia Canturosas reports that bus services have stopped “due to the situation in the city”. He reported “dangerous situations in various parts of the city”.

In videos posted on social media, gunfire could be heard in Nuevo Laredo in the pre-dawn hours.

By noon on Monday, the mayor wrote on Twitter: “the situation in the city is starting to normalize.”

Many Mexican cartels react to the arrest of senior members by creating chaos, either to avoid arrest or transfer of suspects or to pressure authorities to release them. López Obrador said the suspect had already been taken to Mexico City.

It was the second time this year that Nuevo Laredo has been hit by cartel violence following the arrest of a capo.

In March, gunfire and burning vehicles in Nuevo Laredo prompted U.S. officials to close the U.S. consulate and briefly shut down border crossings in Laredo.

The events in March followed the arrest of another leader of the “Teams of Hell,” Juan Gerardo Treviño, the nephew of jailed Zetas leader Miguel Angel Treviño.