The newspaper El Universal published a video that it said was of a pursuit and armed clash in the northeastern border city of Nuevo Laredo that left a dozen suspected criminals dead.

In the footage, reported to have been filmed on July 3 from a military vehicle, men in uniforms are seen approaching a pick-up truck after intense gunfire has subsided.

A shout of "he's alive!" is heard, followed by "kill him, kill him" and an expletive.

"There was a report of a possible crime committed by a member of the army when he finished off a wounded man," Lopez Obrador told reporters.

"Today I gave instructions to the defense minister to investigate it. We're not going to allow these practices."

Members of the Mexican security forces have been accused on several occasions of torture, human rights violations and extrajudicial killings since a controversial anti-drug operation began in 2006.

Before coming to power in 2018, Lopez Obrador was a vociferous critic of the campaign and vowed to send the military back to the barracks.

But the armed forces have continued in their role of tackling gang-related violence, although Lopez Obrador says he has instructed them to respect human rights.