MEXICO CITY (Reuters) - Mexico's deputy foreign minister, Jesus Seade, said on Saturday he sent a letter to the top U.S. trade official expressing surprise and concern over a labour enforcement provision proposed by a U.S. congressional committee in the new North American trade deal.

Top officials from Canada, Mexico and the United States on Tuesday signed a fresh overhaul of a quarter-century-old deal, aiming to improve enforcement of worker rights and hold down prices for biologic drugs by eliminating a patent provision.