The incident occurred on Monday on a highway in Tamaulipas, considered one of Mexico's most dangerous states due to the presence of gang members involved in drug and migrant trafficking.

Numerous violent clashes involving security forces in Tamaulipas have prompted accusations of extrajudicial killings.

The troops involved in the latest deadly incident have been "placed under investigation", an official with the attorney general's office told AFP on condition of anonymity.

A defense ministry statement said the group of soldiers was traveling on a highway when a white pickup truck "tried to ram" one of the army vehicles.

The troops sensed a threat and "used their weapons," the ministry said, adding that five civilians died on the spot and a sixth on the way to hospital.

In March, four Mexican soldiers were sentenced to 40 years in prison for the killing of five civilians in 2023 in Nuevo Laredo, a crime-plagued city bordering the United States.