The United States is making final arrangements with Japan for both parties to sign a contract next month for Tokyo's purchase of four F-35 stealth fighters, a top U.S. Navy officer indicated Tuesday.

Vice Adm. David Venlet signalled this at a hearing of the Senate Armed Service Committee's Subcommittee on Airland. Japan wants the four F-35s delivered in fiscal 2016.

If the two governments seal the contract, it will pave the way for the delivery in 2016, Venlet said. He added that the software program to be installed on the F-35 will be completed that year as well.

Concerns have been rising in Japan that the F-35 development and delivery may face delays and the price of the aircraft may go up. Even after Tokyo formally picked the F-35 as its next-generation mainstay fighter, Defense Minister Naoki Tanaka has signaled in Diet debate that the procurement could be canceled.

Japan plans to eventually have 42 F-35s. After the congressional hearing, Venlet told reporters the estimated price of $10 billion for the 42 fighters includes training and maintenance costs and is thus appropriate for Japan.

But he declined to reveal the unit price.

Japan announced in December it had chosen the F-35 for the Air Self-Defense Force's next-generation fighter.

In Tokyo, Chief Cabinet Secretary Osamu Fujimura said at a press conference that Japan will urge the United States to stick to the initial price tag of ¥8.9 billion per aircraft.

The Defense Ministry estimates the principal fuselage itself to cost around ¥8.9 billion, while the price would be ¥9.9 billion per aircraft, including spare parts.

Tokyo hopes Washington will sign the contract by the end of next month, Fujimura said.