The patrol found 33 migrants from countries including Egypt, Nepal, Cuba, India and Pakistan, it said, without specifying the nationalities of those killed in the incident late Tuesday in Chiapas state.

The two soldiers who opened fire have been removed from their duties pending an investigation, according to a statement.

It said the patrol saw a vehicle -- followed by two flatbed trucks like those used by criminals -- traveling at high speed and apparently attempting to flee.

"Military personnel reported hearing gunshots, so two soldiers activated their weapons, stopping one of the flatbed trucks," the statement said.

Four of the migrants died at the scene while two of the 12 injured lost their lives at the hospital, it added.

The 17 migrants who were unharmed were handed over to the immigration authorities, the statement said.