Authorities say Joaquin 'El Chapo' Guzman, the reputed leader of the Mexican cartel, has given his associates the OK, if necessary, to open fire across the border.

The reputed head of Mexico's Sinaloa drug cartel is threatening a more aggressive stance against competitors and law enforcement north of the border, instructing associates to use deadly force, if needed, to protect increasingly contested trafficking operations, authorities said.

Such a move by Joaquin "El Chapo" Guzman, Mexico's most-wanted fugitive, would mark a turn from the cartel's previous position of largely avoiding violent confrontations in the U.S. -- either with law enforcement officers or rival traffickers.