OTTAWA - Donald Trump's trade czar says U.S. negotiators will take a "do-no-harm" approach to renegotiating NAFTA amid fears that altering the deal could hurt many American agricultural sectors.

U.S. Trade Representative Robert Lighthizer repeated the remarks several times as he testified before a House of Representatives committee.

Lighthizer says his objective is to modernize outdated aspects of the 23-year-old agreement, while protecting the gains U.S. farmers and ranchers have been reaping from the deal.

His remarks come as Prime Minister Justin Trudeau tells the New York Times in an interview that NAFTA has been improved a dozen times over the years and will be updated once again to adjust to new challenges.

Earlier this week, Lighthizer said the U.S. plans to move very quickly on NAFTA talks, which can begin as early as Aug. 16.

He has also indicated he has no deadline to complete the negotiations because the Trump administration's top priority is nailing down the best deal possible for the U.S.