OTTAWA, Ontario — The most contentious issues in talks to renegotiate the North American Free Trade Agreement have not been introduced by the United States, the Canadian foreign minister said Wednesday as the third round of talks between Canada, the U.S. and Mexico concluded.

U.S. Trade Representative Robert Lighthizer said some issues related to small- and medium-size enterprises were resolved, but an enormous amount of work still needs to be done on other, difficult matters. He said delegates made significant progress on competition policy, digital trade, state-owned enterprises and telecommunications. Details on the treaty chapter they agreed on were not available.

Canadian Foreign Minister Chrystia Freeland said that on potentially the most difficult areas the U.S. has not introduced formal proposals or text. Freeland said Canada can’t respond to something that has not been introduced.

Mexican Economy Secretary Ildefonso Guajardo also said “substantial challenges” lie ahead.

U.S. President Trump has called the 1992 trade deal the worst in history.

“We all know that this is an administration that is openly protectionist. It’s an administration that speaks quite openly of the America-first policy. That is the reality that Canada has to deal with,” Freeland said.

A fourth round of negotiations is scheduled for Oct. 11-15.

Asked if she thinks the U.S. really wants a deal, Freeland answered: “I do not have the superpower that allows me to look into the heart of a counter party and divine their true intention.”

Dan Ujczo, an Ohio-based international trade lawyer who represents companies in both the U.S. and Canada, said there was pessimism among about 250 stakeholders and negotiators who attended a reception in Ottawa on Tuesday night.

“The general mood is not if, but when, we will see a withdrawal (from NAFTA by the U.S.). My view is likely later this year,” Ujczo said.

The United States wants to eliminate NAFTA’s Chapter 19 private arbitration panels, while Canada wants to keep them. The panels can overrule tariffs, making it harder for the U.S. to unilaterally block products.

Mexico’s low wages have also become an increasing point of debate. Mexico has drawn plants and investments by capitalizing on low wages and weak union rules, and Mexican business and labor leaders appear to be resistant to any attempt to tighten labor standards or ensure that Mexican wages rise.