China’s "fifth-generation" Chengdu J-20 fighter jet has led to sales interest in the US F-35 Joint Strike Fighter in the Asia-Pacific region, the Wall Street Journal reported. Tom Burbage, Lockheed Martin’s general manager for the F-35 fighter program, said that Japan, Singapore and South Korea have begun negotiations with the US government for the F-35 jet. While no countries have yet signed agreements, government officials have indicated strong interest in the F-35, a variant of Lockheed’s F-22 Raptor designed for international sales, Burbage said. Lockheed’s rival Boeing is also getting in on the interest with its upgraded F-15E stealth fighter. Speculation mounted over the weekend that the J-20 may have used technology from an American F-117 Nighthawk shot down over Serbia in 1999.