The top trade representatives of the United States, Mexico and Canada have ended the latest round of talks on renegotiating the North American Free Trade without a deal, days before an unofficial deadline to get any deal through the U.S. Congress.

Mexico's Economy Secretary said Friday working groups from the three countries would meet again Monday. But Thursday marks the last day under procedural deadlines to get a vote under the current U.S. Congress.

Mexico disagrees with U.S. attempts to get higher regional content rules and orient production to higher-wage U.S. and Canadian factories.

A Mexican official who was not authorized to be quoted by name said the trade representatives would remain "on call." But he said it was difficult, and suggested the U.S. would have to show more flexibility.