TOKYO -- Japan plans to choose the U.S. as its partner for developing the successor to the F-2 fighter jet, while taking on most of the R&D costs to avoid leaving essential design information solely in American hands again, Nikkei has learned.

Tokyo was weighing the U.S. offer against a U.K. proposal that would have guaranteed it the freedom to update the new planes at will. But ultimately, it decided to stick with its top ally given that their security ties have significantly expanded in scope in recent years. An official decision will made within this year.

"Ensuring we can freely modify and upgrade [the new jets] in the future is extremely important," Defense Minister Taro Kono said. Japan's inability to freely update the F-2 has limited the usability of much of its fleet.

Japan's defense industry is envisioned as playing the central role in the project, which is expected to cost tens of billions of dollars. Deployment of the new jets is now slated for the mid-2030s.

The government has been in talks with the U.S. and U.K. on the project since last summer, with American contractors Lockheed Martin and Boeing and London-based BAE Systems named as possible partners.

The move toward the American bid comes amid deepening defense cooperation between Tokyo and Washington. As joint defense exercises between the two expand both in number and in content, Tokyo needs more advanced tactical networks that are compatible with those used by the U.S. military. A Defense Ministry proposal for the jet project last year cited the need for interoperability.

Japan looks to create a completely new manned aircraft, opting against a Lockheed Martin proposal for a hybrid of the F-22 and F-35. Tokyo will stick with domestic development for the plane's mission systems, which control such crucial equipment as radar, sensors and electronic warfare gear. It will not limit itself to a single American partner company.

Japan opted against picking the U.K. as a main partner for the project, concluding that even a three-way arrangement would not let the Japan-U.S. alliance maintain its technological edge.

But it does look to share technology with London, which is working on its own next-generation fighter, the Tempest, and has inquired about working with Tokyo on developing systems and electronic components.

On the domestic side, Japanese companies have begun research into high-output engines and powerful but compact radar systems that can detect stealth fighters. Participants in the project are expected to include Mitsubishi Heavy Industries, Toshiba and IHI.

The plan could take some twists and turns before Tokyo makes the final call. Japan was initially set to lead development of the F-2 when the project first came up in the 1980s, but the U.S. took over as trade tensions between the allies led Washington to pressure Tokyo to buy American.

As a result, design details of components considered to be sensitive were not disclosed to the Japanese side, hamstringing its ability to modify the jets on its own.

U.S. President Donald Trump, who has demanded that Japan take on more the cost of hosting American troops, has reportedly expressed interest in the new project. Negotiators will continue working to hammer out each side's share of the development costs as well as production.