Japan may purchase additional F-35 fighter jets if their procurement costs fall, Defense Minister Itsunori Onodera said Tuesday after visiting a Lockheed Martin Corp. assembly plant in Fort Worth, Texas.

"If the unit price falls, it may be important to reconsider the number of fighters (Japan will buy)," said Onodera, who held talks with senior officials from Lockheed Martin at the factory.

As the successor to the aging F-4 Phantom operated by the Air Self-Defense Force, the F-35 has advanced stealth capabilities and can escape radar detection. The ASDF currently has 42 of them on order.

The Defense Ministry and the ASDF also need to replace roughly half of the 200 or so aging F-15 fighter jets currently in operation, and Onodera's remarks suggest that the government might favor the F-35 as a replacement.

A five-year defense program, in operation through fiscal 2018, says Japan will "consider replacing those F-15s that do not get refurbished with more advanced fighters."

Last Thursday, the U.S. Department of Defense said it was grounding the country's entire fleet of F-35 fighter jets for engine inspections, after one caught fire as it prepared to take off in Florida in late June.