Talks to rework the North American Free Trade Agreement (NAFTA) are not sufficiently advanced for the United States, Mexico and Canada to announce a deal "in principle" at this month's Summit of the Americas in Lima, according to two people familiar with matter.

The ministers responsible for NAFTA met on Friday in Washington, and said progress had been made on reworking the accord.

But there was still too much to do for an agreement to be unveiled at the April 13-14 summit, the sources said, speaking on condition of anonymity due to the sensitivity of the matter.