A family of six, including three children, were killed Friday by gunmen in the southern Mexico border state of Chiapas in a town marred by cartel-backed militia violence.

Julio Pérez, the mayor of the Chiapas town of Pantelho, said the killings happened there Friday, and called it “a massacre.” Two warring militia groups suspected of being backed by drug cartels have been battling for control of the town.

In a brief statement, the state prosecutor’s office said three suspects were arrested but neither the victims nor the detainees have been identified.

It was the latest in a string of mass killings in which hitmen have wiped out entire families in Mexico.

On Sunday, gunmen burst into a home in the north-central state of Guanajuato and killed four women and two children.

Both Chiapas, which shares a border with Guatemala, and Guanajuato have been hit by bloody gang turf battles in recent years.

Local media reported that the gunmen entered the home in the city of Leon in Guanajuato looking for a male member of the family. When they found out he had already fled, they killed the women and children.

The Guanajuato killings have drawn special attention because surveillance camera footage showed five National Guard officers entering the home five minutes before the killings took place. They left the home carrying a large black plastic bag just before the killers arrived.

On Friday, President Andrés Manuel López Obrador said five officers of the quasi-military National Guard had been detained for breaches of military discipline, and were in the custody of the Defense Department, but he refused to give more details on the case.

Chiapas, where the family was killed Friday, has been plagued by recent violence, especially in the weeks leading up to the June 2 presidential elections.

Last month, officials said two attacks against mayoral candidates in Mexico’s elections left nine people dead in Chiapas. Just days before that, six people, including a minor and mayoral candidate Lucero Lopez, were killed in an ambush after a campaign rally in Chiapas. Around the same time, 11 people were killed in mass shootings in a village in the township of Chicomuselo, Chiapas.

The situation in Chiapas has deteriorated because of a war being waged between the Jalisco New Generation and Sinaloa cartels in a region known as La Frailesca, which includes Villa Corzo and La Concordia.

Claudia Sheinbaum became the first woman to win the country’s presidency earlier this month. Two female politicians have already been killed in Mexico since Sheinbaum’s historic election.