The United States is upgrading Malaysia from the lowest tier on its list of worst human trafficking centers, U.S. sources said Wednesday, a move that could smooth the way for an ambitious U.S.-led free-trade deal with the Southeast Asian nation and 11 other countries.

The upgrade to so-called "Tier 2 Watch List" status removes a potential barrier to President Barack Obama's signature Trans-Pacific Partnership (TPP) deal.

A provision in a related trade bill passed by Congress last month barred from fast-tracked trade deals Malaysia and other countries that earn the worst U.S. human trafficking ranking in the eyes of the U.S. State Department.