Mexico has expressed that it wants an immediate investigation into how U.S. military-grade weapons have ended up in the hands of Mexican drug cartels. The nation’s military has discovered belt-fed machine guns, rocket launchers, and even grenades, according to the Associated Press.

The weapons the Mexican military has discovered are not available for retail to Americans, which raises questions about how drug cartels have them.

Foreign Relations Secretary Alicia Barcena said that “the [Mexican] Defense Department has warned the United States about weapons entering Mexico that are for the exclusive use of the U.S. army.”

“It is very urgent that an investigation into this be carried out.”