(Updates to add comments, background and details on trade case)
By Chris Prentice
NEW YORK, Nov 6 (Reuters) - A U.S. sugar growers group has said that "serious issues" still need to be resolved with a U.S.-Mexico trade pact designed to suspend prohibitive duties on Mexican imports.
The American Sugar Coalition, which represents the petitioners on the case, has asked the U.S. government to extend the Nov. 10 deadline for comments on the proposed agreement, according to documents filed by the group's counsel on Thursday.
The issues included defining refined sugar, according to the Nov. 6 letter to the U.S. Department of Commerce.
The United States and Mexico hammered out a draft suspension agreement last week designed to avert duties on Mexican imports expected to curb key supplies into the coveted U.S. market.
"Put simply, these are complicated agreements and we believe more time is necessary to consider how to make them workable and effective," the American Sugar Coalition's counsel said in the Nov. 6 letter.
Lawyers for the Sweetener Users Association and for Imperial Sugar, a major U.S. refinery owned by agricultural merchant Louis Dreyfus Commodities, also requested an extension earlier this week.
The Mexican industry's counsel told the Commerce Department that they opposed those requests, saying in a Nov. 5 letter that it is in the "collective public interest" to resolve the dispute as "expeditiously as possible."
A spokesperson for the American Sugar Coalition did not respond immediately to a call for comment.
Reporting by Josephine Mason; Editing by Diane Craft and Andrew Hay