A further 3,900 residents of Indonesia's Sumatra Island on Friday will add their names to a lawsuit targeting the legitimacy of Japanese overseas aid, their lawyer said Tuesday.

They will join 3,900 of their neighbors who initially filed the suit at the Tokyo District Court in September.

The plaintiffs claim that around 20,000 island residents were forcibly resettled to areas lacking proper living facilities and job opportunities when the hydroelectric Kotopanjang Dam, funded via Japanese official development assistance, was completed in 1996.