A judge ordered the troops to be held in preventive detention, according to Federal Judiciary Council sources.

The soldiers are accused of opening fire at a vehicle in which seven people were traveling early on February 26 in Nuevo Laredo, which is regularly the scene of violence attributed to drug traffickers.

Five of the civilians died, another was injured and a seventh was unharmed.

The military said that the troops were carrying out a routine patrol when they heard gunshots and saw a pick-up truck without lights or license plates whose driver accelerated suddenly and collided with a parked vehicle.

Hearing a noise, the military personnel fired their weapons, it said.

The National Human Rights Commission has accused the soldiers of using excessive force.

According to New York-based advocacy group Human Rights Watch, the deployment of Mexican soldiers for law enforcement and to fight organized crime has led to widespread human rights violations.

Since taking office in 2018, President Andres Manuel Lopez Obrador has given increased responsibility to the armed forces, in addition to their public security role, including control of ports and customs and major infrastructure projects.