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 Nuevo Laredo Human Rights Committee, a local civil society group, the young men were traveling in a truck after leaving a nightclub when they were shot by soldiers.

For its part, the defense ministry said the troops were carrying out a routine patrol when they heard gunshots.

The pick-up truck, carrying seven people, accelerated as the soldiers approached, the army statement added.

It 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 the ministry, which announced an internal investigation.

According to the Nuevo Laredo Human Rights Committee, the vehicle received 20 bullet holes and one of the deceased was a US national.

Videos posted on social media showed a confrontation between relatives of the young men, residents and soldiers who fired warning shots.

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.