MEXICO CITY, Feb. 13 (Xinhua) -- Negotiations to update the two-decade North American Free Trade Agreement (NAFTA) could continue until next year, the Mexican Institute of Financial Executives (IMEF) said on Tuesday.

NAFTA partners Mexico, the United States and Canada started the talks in August, expecting to have a revamped agreement by the end of 2017. But the negotiations turned out to be more complicated, and now political events threaten to prolong the process, said IMEF President Fernando Lopez.

"There are obvious scheduling reasons that would make even the most optimistic scenario of reaching a deal by the end of March, impossible," Lopez told reporters at a press conference.

Mexico's coming general elections in July "are an obvious obstacle to closing the deal," he said, referring to potential changes in leadership and lawmakers.

By Sept. 1, Mexico will have a new president-elect and new members of Congress, which might not be on board with the contents of the agreement, he said.

Some 3,400 elected posts will be disputed in the coming elections, making them the largest in Mexico's history, said Lopez.

Meanwhile, the U.S. Congress gave the current administration of President Donald Trump until June 30 to fast track the renegotiation of NAFTA under the so-called Trade Promotion Authority (TPA) legislation.

"The renegotiation of NAFTA will depend on the extension of the TPA in the United States," said Lopez.

"It would be wise for the Mexican government to start signalling that NAFTA's conclusion will be postponed until 2019," Lopez added.

The seventh round of talks are to take place in Mexico City Feb. 26 to March 6, with Mexico's government hoping to wrap up the sections on sanitary and phytosanitary measures, telecommunications and technical obstacles to trade.

Three other chapters have been completed, but several key issues have escaped consensus, including bringing Mexican wages in line with North American standards; rules of origin that specify how much imported content goes into a car manufactured in NAFTA territory; and having a sunset clause to renegotiate the deal every five years.