Japan Defence Minister Naoki Tanaka on Friday said his ministry has asked the United States to stick to the initially agreed price of the F-35 stealth jet, which Japan has picked as its next-generation mainstay fighter. \"Naturally, our position is (for the US) to adhere to its proposed price,\" Tanaka told reporters, adding \"We are strongly requesting this.\" The ministry has indicated in a letter to the US Department of Defence the possibility of halting the F-35 purchases if prices skyrocket. 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. Japan announced in December that it had decided on the F-35, which is being developed by an international consortium led by US aircraft maker Lockheed Martin Corp. The ministry plans to procure four F-35 jets in fiscal 2012 starting April. In that fiscal year, each aircraft has been estimated to cost about JPY 8.9 billion, or JPY 9.9 billion per aircraft including spare parts.