The defense ministry said in a statement it was working with investigators to clarify the events that occurred early Sunday in the border city of Nuevo Laredo.

According to a complaint from the National Human Rights Commission (CNDH), the young men were traveling in a van after leaving a nightclub when they were shot by soldiers.

For its part, the defense ministry said the soldiers were carrying out a routine patrol when they heard gunshots. The van accelerated as the soldiers approached, the army statement added.

The van collided with a parked vehicle, and upon hearing the noise, the military personnel "activated their weapons," it said.

Five occupants died, another was wounded and a seventh was unscathed, according to figures from the ministry, which announced an internal investigation.

According to the CNDH complaint, the vehicle received 20 bullet holes and one of the deceased was a US national.

Videos posted on social media showed an exchange of fire purportedly between soldiers, relatives of the young people and local residents.

The footage also showed what appeared to be a soldier being trampled on the ground by several people and another being punched in the face.

Nuevo Laredo is regularly the scene of violence attributed to drug traffickers.

On December 7, the authorities announced the deaths of seven suspected criminals in clashes with soldiers.