Mexican Economy Minister Ildefonso Guajardo (C), U.S. Trade Representative Robert Lighthizer (R), and Canadian Foreign Minister Chrystia Freeland pose for photos during a press conference after the seventh round of talks to modernize the North American Free Trade Agreement (NAFTA), in Mexico City, capital of Mexico, on March 5, 2018. The seventh round of talks to modernize NAFTA ended here Monday on a mixed note with the U.S. calling the progress not good enough but Mexico remaining upbeat. (Xinhua/Francisco Canedo)

MEXICO CITY, March 5 (Xinhua) -- The seventh round of talks to modernize the North American Free Trade Agreement (NAFTA) ended here Monday on a mixed note with the U.S. calling the progress not good enough but Mexico remaining upbeat.

U.S. Trade Representative Robert Lighthizer said only six of NAFTA's 30 chapters have been closed so far.

"We have not made the progress many had hoped," he said, adding, "Our time is running very short. I fear that the longer we proceed, the more political headwinds we will feel."

Lighthizer told the press that the upcoming Mexican presidential elections, U.S. mid-term elections, and provincial elections in Canada's Ontario and Quebec were complicating matters.

However, Mexican Economy Minister Ildefonso Guajardo said the seventh round of talks had created "an adequate landing strip" for a successful resolution.

Differences in unresolved chapters such as e-commerce, telecommunications, energy and technical obstacles to trade were only "minimal", he said, adding, "As we move forward, we will begin to fulfill our objectives and close our differences."

Countering Lighthizer's call for haste, Guajardo said Mexico will take the time it takes, at least until the mandate of President Enrique Pena Nieto ends on Nov. 30.

"This isn't over until it's over. We will negotiate as far as we have to," he said.

Canadian Foreign Minister Chrystia Freeland said there is still hard work ahead for a successful updating of NAFTA.

In the next five weeks, before the eighth round of talks starts in April, negotiators will meet to resolve the thorniest issues, such as the clause to terminate NAFTA and the rules of origin in the automobile sector.

Canada, the United States and Mexico have been carrying out intense negotiations to redraft NAFTA since August 2017 after U.S. President Donald Trump said the deal has been unfair to the United States.