The US military has significantly increased its surveillance of Mexican drug cartels over the past two weeks, with sophisticated spy planes flying at least 18 missions over the southwestern US and in international airspace around the Baja peninsula,

An internal memo shows that Mexican cartels are ordering cartel members to attack Border Patrol agents with explosives and kamikaze drones.

Over the course of 10 days, spy planes flew at least 18 missions over the southwestern U.S. and the international airspace around the Baja peninsula, according to three officials.