Japan will launch a tender for fighter jets as soon as midmonth, the Defense Ministry said, in a deal seen worth up to $40 billion (¥4.12 trillion) as Tokyo seeks to bolster its air defenses amid creeping tension with China over disputed maritime borders.

In one of the biggest fighter jet contracts up for grabs in years, a ministry spokesman said Japan will contact foreign and domestic defense contractors soon after a July 5 deadline for expressions of interest in the tender for about 100 warplanes.

People familiar with the matter said U.S. firms Boeing Co. and Lockheed Martin Corp. have been invited to take part in the project, dubbed the F-3 fighter jet program, alongside Mitsubishi Heavy Industries Ltd., the prime domestic contractor.