(Adds report details, AMIA director quotes, background on NAFTA talks)
MEXICO CITY, Aug 6 (Reuters) - Mexican automobile exports, excluding those made by Nissan, fell 5.5 percent in July year-on-year on weaker U.S. sales, while output for the month fell 3.7 percent, partially due to flooding at a Honda plant, auto industry association AMIA said on Monday.
Mexico exported 214,984 units in July, down from 227,444 the same month a year earlier, AMIA said, while producing 291,577 units, a fall from 302,716 in July a year before.
AMIA's export data did not include Japanese carmaker Nissan Motor Co Ltd, which has stopped providing export figures.
"The trend in the United States is a flattening in sales," AMIA's director Fausto Cuevas told reporters on Tuesday, without providing details.
Flooding at a Honda Motor Co facility in Mexico weakened overall production data, Cuevas added, without specifying which plant was affected. Local media reported in early July that a river had spilled into Honda's plant in the state of Guanajuato, halting production.
Production data showed slumps at Audi AG, Ford Motor Co, Kia Motors Corp and Nissan. Cuevas did not have details on the causes.
Domestic auto sales slipped 6.4 percent to 114,312 vehicles in July compared with the year earlier period, AMIA added.
Uncertainty has dogged Mexico's auto industry for the past year since U.S. President Donald Trump threatened to pull out of the North American Free Trade Agreement with Mexico and Canada unless it was reworked to send manufacturing jobs to the United States.
The Trump administration also wants Mexican workers to be paid more and is demanding more North American content in cars and light trucks produced in the NAFTA nations.
Cuevas said that the private sector's position is that "nothing is resolved until everything is resolved," and that no agreements have been reached in talks that resumed in late July between Mexican and U.S. cabinet ministers in Washington. (Reporting by Sharay Angulo, Writing by Daina Beth Solomon, Editing by Michael O'Boyle and Cynthia Osterman)