Japan is considering beginning development of next-generation fighter jet in fiscal 2020 — one year earlier than planned — to succeed the Air Self-Defense Force's F-2s, which are expected to be retired in the 2030s, governmental sources said Wednesday.

The Defense Ministry had intended to earmark costs for the development starting with the budget for the year from April 2021. Lawmakers, however, said that might be too late and the ministry is set to move up the schedule by a year, according to the sources.

The ministry will specify the amount before the Cabinet endorses a fiscal 2020 draft budget by the end of this year.

Japan has been considering co-developing the fighters with U.S. or British companies, the sources said, noting U.S. defense giant Lockheed Martin Corp. may be the top option for a partner.

A "hybrid model" of the U.S. military's stealth F-22 and F-35 fighter jets, both of which were partly developed by Lockheed Martin, is thought to be a possibility.

But there is concern in the United States about the possible leakage of state-of-the-art technologies, making joint projects difficult, the sources said.

Under its latest Medium Term Defense Program covering the five-year period from April, the ministry has said that it will "launch a Japan-led development project at an early timing with the possibility of international collaboration" for a successor to the F-2.