In an unexpected move, Japan has asked Indonesia to compensate villagers on Sumatra who were forcibly resettled from their land to make way for a Tokyo-funded hydropower dam, diplomatic sources said Tuesday.

Japan takes issue with Indonesia's failure to fulfill pledges to provide replacement rubber plantations and clean well water to villagers displaced by the Kotopanjang Dam project, according to the sources.

Jakarta has received the request and is now accelerating measures to aid the villagers, they said.

The request follows reports that some 3,000 people from 13 villages on the island plan to file a lawsuit with the Tokyo District Court against the Japanese government for losses they suffered due to the forced resettlement.

The threatened legal challenge would be the first over a project paid for by Japan's official development assistance.

Kotopanjang Dam, built on a protected forest and traditionally owned land in the provinces of Riau and West Sumatra, was completed in 1997 at a cost of 36.4 billion yen. Of that amount, 31.18 billion yen was paid for by a yen-denominated government loan.

As a result of the construction, 12,400 hectares of fertile valley land have been submerged and 4,866 families displaced.

The villagers have been left without proper living facilities, including clean well water, on the resettled land, and have not been guaranteed job opportunities there, becoming "developmental refugees," according to their supporters.

The dam has also damaged the natural environment in the area, with elephants and other animals facing starvation, they said.

Japanese government sources said the aid project was meant to serve as a "model case" where the recipient country would fulfill such conditions as obtaining the consent of villagers to resettle and preserving the environment.