WASHINGTON — The renegotiation of the North American Free Trade Agreement is off to a rocky start.

The Trump administration lectured Canada and Mexico on the failures of the current agreement at an opening news conference Wednesday morning, while behind closed doors negotiators began to seek significant concessions from America’s neighbors.

“We feel that Nafta has fundamentally failed many, many Americans and needs major improvement,” said Robert Lighthizer, the United States trade representative, who is leading the United States team aiming to overhaul the 25-year-old agreement.

The Canadian and Mexican representatives were publicly pleasant, emphasizing their commitment to regional trade and the benefits resulting from a regional alliance. But both nations also say the current agreement is not tilted against the United States.