MEXICO CITY (AP) — The killing of two utility workers in northern Mexico may be related to the scorched-earth tactics of warring drug cartels, Mexico’s president said Thursday.

Drug cartels in Mexico have increasingly targeted civilian communities in their turf battles, isolating towns that don’t support them by cutting off roads and electricity, or forcing residents to leave.

On Tuesday, assailants opened fire on two trucks carrying workers from the state-owned electrical power company on a highway. Two workers escaped and two were killed.

On Thursday, President Andrés Manuel López Obrador said the area in the northern border state of Sonora was the scene of fighting between gangs, who had cut electricity to two villages as “reprisals.”

“There is fighting between groups there,” López Obrador said of the area around the village of Onavas, where the attack occurred.

While he said the attackers might have mistaken the utility trucks for those of a rival gang, López Obrador noted “there is another hypothesis that suggests they were performing their duties by going to reconnect electricity to two villages that had been cut off by one of the groups as reprisals.”

In the western state of Michoacan, warring drug cartels have periodically cut off villages that appear to support a rival gang, by downing power lines or digging trenches across roadways.

But the attack Tuesday was unusual, because up to now cartels have largely avoided going after public workers trying to reconnect roads or power lines. Moreover, resuscitating the debt-strapped state-owned utility, the Federal Electricity Commission, has been one of López Obrador’s main policy initiatives.

Drug cartels — including the La Linea gang based in Ciudad Juarez and factions of the Sinaloa cartel — have been fighting over the lucrative drug-producing and shipping zones of Sonora state for years.

The cartel conflict may have played a role in the 2019 ambush slayings of nine U.S.-Mexican dual citizens in a rural area relatively near Onavas.

The three women and six children from the extended Langford, LeBaron and Miller families were ambushed and slain by suspected drug gang assassins on Nov. 4, 2019.

Initial investigations suggested a squad of gunmen from the La Linea gang had set up the ambush to kill members of the rival cartel. However, relatives of the victims say that at some point, the gunmen must have known who they were killing.