MANASSAS, Virginia, May 22 (Reuters) - U.S. Trade Representative Jamieson Greer said on Friday that the first round of formal negotiations to update the U.S.-Mexico-Canada trade agreement next week in Mexico City will focus on strengthening regional rules of origin and economic security provisions.

He told reporters at a Micron Technology memory chip plant in suburban Washington that regional content rules needed to be changed to help re-shore U.S. manufacturing, adding: "If you're going to get a special deal on trade with the United States of America, we want to make sure that there's U.S. content in that."

Greer added that he was aware of automakers' calls to keep the six-year-old USMCA a trilateral trade deal. Next week's talks will be between the U.S. and Mexico only and exclude Canada.