A Pacific Rim trade agreement may have to proceed without Japan if Tokyo fails to open its agricultural markets to imports, U.S. Agriculture Secretary Tom Vilsack said.

"It is incumbent upon us to have market access, and if the Japanese are unwilling and unable to provide that market access, then the other alternative is that you have a less comprehensive agreement in which the Japanese are not part," Vilsack told reporters and editors in Washington on Monday.

"We don't want that. We think it's really important for the benefit" of the Trans-Pacific Partnership deal "that Japan be part of this."