Mexico wants an urgent investigation into how U.S. military-grade weapons are increasingly being found in the hands of Mexican drug cartels, Mexico’s top diplomat said Monday.

Mexico’s army is finding belt-fed machine guns, rocket launchers and grenades that are not sold for civilian use in the United States.

“The (Mexican) Defense Department has warned the United States about weapons entering Mexico that are for the exclusive use of the U.S. army,” Foreign Relations Secretary Alicia Bárcena said. “It is very urgent that an investigation into this be carried out.”

The Mexican army said in June that it had seized 221 fully automatic machine guns, 56 grenade launchers and a dozen rocket launchers from drug cartels since late 2018.

The military-grade U.S. weaponry — which cartels have bragged about and openly displayed on social media — poses a special challenge for Mexico’s army, which along with police and the National Guard already faces cartels operating homemade armored vehicles and bomb-dropping drones.