TOKYO (Kyodo) -- The Defense Ministry has indicated to the U.S. Department of Defense the possibility of halting purchases of the F-35 stealth jet, which Japan has picked as its next-generation mainstay fighter, if prices skyrocket, sources close to Japan-U.S. ties said Wednesday. In a letter dated Feb. 13, the ministry expressed its concern to the Pentagon over a rise in the price tag of the F-35, which is being developed by an international consortium led by U.S. aircraft maker Lockheed Martin Corp., the sources said. The ministry also requested a review of the procurement system under a foreign military sales arrangement that allows the United States to change prices at its discretion, the sources said.