An auto transport carrier crosses the Ambassador Bridge heading to the United States in Windsor, Ontario, Canada, on Aug. 16, 2017. The United States, Canada and Mexico on Sunday wrapped up the first round of renegotiations on the North American Free Trade Agreement (NAFTA), pledging to continue a rapid pace of talks in the coming months to update the 23-year-old trilateral trade deal. (Xinhua/Zou Zheng)

MONTREAL, Jan. 29 (Xinhua) -- Canada, the United States and Mexico concluded Monday their sixth round of North American Free Trade Agreement(NAFTA) negotiations in Montreal with a chapter of anti-corruption but still at odds on other key issues.

At a joint press conference following the talks, Canadian Foreign Affairs Minister Chrystia Freeland, U.S. Trade Representative Robert Lighthizer and Mexican Secretary of Economy Ildefonso Guajardo Villarreal told a press conference that some progress had been made while acknowledging that tough challenges still lie ahead to strike a new deal.

They separately introduced the sixth round talks and none of them answered questions at the press conference.

Freeland said Canada prefers a negotiated settlement, but will protect the domestic softwood lumber industry. She said Canadian challenging the U.S. at the World Trade Organization last month is a separate issue from the NAFTA talks. In the challenge, Canada cited other examples of alleged U.S. wrongdoing, almost all of them concerning other trading partners, such as China, India, Brazil and the European Union.

"Canadians do not view free trade as a zero sum game in which one side must lose in order for the other to win," she said.

Lighthizer said some progress had been made, hoping it will accelerate and achieve major breakthroughs. "This round was a step forward, but we are progressing very slowly."

At the press conference, Lighthizer also said the trade complaint launched by Canada at the World Trade Organization against the U.S. use of anti-dumping and anti-subsidy duties are "unprecedented" and a "massive attack on all of our trade laws."

Lighthizer also voiced his opposition to two proposals put on the table by Canada, including a rules-of-origin pitch for autos.

"We find that the automobile rules-of-origin idea that was presented when analyzed, may actually lead to less regional content than we have now, fewer jobs in the United States, Canada and most likely Mexico," he said. "This is the opposite of what we were trying to do."

Villarreal said while progress had been achieved, "substantial challenges" remain to overcome.

The sixth round closed on a more conciliatory note than expected, with all three countries looking forward to more progress on the next round of talks, which will be held in Mexico City late February.

Before NAFTA sixth round talks, some experts and politicians said U.S. President Donald Trump would announce that U.S. will withdraw from NAFTA.