“We remain concerned about the lack of progress in the negotiations between the Republic of Korea and the U.S. Air Force on the KF-16 Upgrade Program that has now resulted in a partial stop work order," said Brian Roehrkasse, spokesman for the U.S. unit of the British company.

South Korea last week said it could cancel the overall project to upgrade 134 F-16 fighter jets and seek a different contractor, after the U.S. Air Force told Seoul the projected cost of 1.75 trillion won (1.05 billion pounds) could rise by 800 billion won.

(Reporting by Andrea Shalal; Editing by Lisa Shumaker)