U.S. Trade Representative Ron Kirk has reiterated the stance that differences in automobile trade must first be settled before the Korea-U.S. free trade agreement can be ratified.

In a speech at a forum hosted by the Detroit Economic Club, Kirk blamed lackluster U.S. car sales in Korea on what he called the history of Korean protectionism in the auto sector.

Kirk said there are questions about whether the FTA will establish a level playing field for U.S. automakers trying to sell their products in Korea.

He said he won't put a deadline on the ratification of the deal.