Tokyo expressed concerned that the F-35 Lightning sales, which contain Japanese components, might violate Japanese legal prohibitions on weapons exports to designated countries.

The F-35 Lightning II is a fifth-generation, single-seat, single-engine Joint Strike Fighters under development by U.S. defense contractor Lockheed Martin Corp.

Japan's draft fiscal 2013 budget adopted by the government this month sets aside $330 million to acquire two F-35s, the first to be manufactured with the participation of Japanese companies.

At a news conference this week in Tokyo Japanese Defense Minister Itsunori Onodera admitted that F-35s that use Japanese parts may be exported to Israel, which would conflict with the government's three principles on arms exports, which ban exports to Communist countries, nations subject to U.N. Security Council arms export embargoes resolutions and countries involved in or likely to be involved in international conflicts.

Regarding the potential impasse, Chief Cabinet Secretary Yoshihide Suga said that maintaining consistency with the ban is "under discussion within the government," Asahi Shimbun reported Wednesday.

In December 2011 Japan chose the F-35 as its next mainstay fighter. Japanese Defense Minister Yasuo Ichikawa said that the decision to buy 42 F-35s, valued by analysts at more than $7 billion, would help Japan adjust to a rapidly changing regional security dynamic.

"The security environment surrounding future fighter jets is transforming," he said. "The F-35 has capabilities that can firmly respond to the changes."

After Japan announced its decision the U.S. Defense Department said in a statement, "The F-35 Program Office looks forward to strengthening partnerships with Japan and contributing to enhanced security throughout the Asia Pacific region."

The U.S. government plans to buy 2,443 F-35s. These will consist of three models: The F-35A is a "conventional" U.S. Air Force fighter; the F-35B is the STOVL version for the U.S. Marines and the F-35C, a naval version with folding wings and specifically designed for carrier operations.

The first F-35A flew in December 2006, the F-35B followed in June 2008, while the naval variant F-35C took to the air in June 2010.

Lockheed Martin Vice President for F-35 Business Development Steve O'Bryan is in no doubt that the F-35 will be a winner for his company, predicting sales of 3,100 F-35s by 2037 when production is to end.

The F-35 is a byproduct of the 1993 U.S. Common Affordable Lightweight Fighter Project, a strictly U.S. venture that three years later became the U.S. Joint Strike Fighter Program, with Britain and other international partners as collaborators, engaged in developing a fifth-generation stealth fighter to replace several frontline aircraft including the F-16 Fighting Falcon, the F/A-18 Hornet and the AV-8B Harrier II.

Not all are enamored of the aircraft, with many critics citing its costs, the highest ever for a single aircraft. Winslow T. Wheeler of Washington's Center of Defense Information recently labeled the F-35 a "gigantic performance disappointment," before adding, "It's the problem of paying a huge amount of money thinking you're getting a Ferrari; you're not, you're getting a Yugo."