The World Trade Organization sees a "challenging" and "difficult" road ahead for international trade liberalization due to the current political climate.

The WTO's director-general says he's confident Mexico and the United States can sort out their current trade difficulties, which include a border-crossing slowdown, U.S. threats to close the border and the still-pending ratification of the U.S.-Mexico-Canada trade agreement.

But Roberto Azevedo said Thursday the fight to expand free trade "is going to be challenging, is going to be difficult, above all because of the political conditions we have in the world today."

Mexico's Economy Secretary said a slowdown on border crossing would affect U.S. consumers because "soon they won't find fresh vegetables on store shelves."