TOKYO - Japan planned to sign a contract with the United States next month for the purchase of four F-35 stealth fighter jets despite a price increase for the aircraft, local media reported Monday.

? The US Marine Corps version of Lockheed Martin's F35 Joint Strike Fighter, F-35B test aircraft BF-2 flies with external weapons for the first time over the Atlantic test range at Patuxent River Naval Air Systems Command in Maryland in a February 22, 2012 file photo. [Photo/Agencies]

The fighter jets are set to be delivered before the end of fiscal year 2016 and may cost about $138 million per unit. The Japanese government is making arrangements with the US for the purchase as part of the budget in the current fiscal year which ends next March.

The Japanese government decided in December to choose the F-35 stealth jet, developed by the United States and eight other countries, as the country's next-generation fighter jet.

Diagram and key features of the Lockheed Martin F-35 fighter jet.?[Photo/Agencies]?

The government originally estimated the price of the jet to be about 9.9 billion yen (about $123 million) per aircraft. The price rose after the US decided to postpone its purchase of the jets due to its defense budget cuts. ?

Lockheed Martin's F-35 Lightning II stealth fighter, which had been reviewed along with Boeing's FA-18 Super Hornet and the Eurofighter Typhoon, will replace the country's 40-year-old fleet of F-4s.