The case was reported a month after corruption allegations in Vietnam led Japan to suspend all assistance to the country.

Japan's Nishimatsu Construction Co. gave the bribe to a senior official in Bangkok's local government with the aim of winning an order to build a drain tunnel, the Asahi Shimbun said, quoting unnamed Thai government sources.

Prosecutors in Tokyo presented evidence to Thai authorities and are seeking cooperation, treating the case as a suspected violation of Japan's law banning bribery to a foreign official, the report said.

A joint venture of Nishimatsu and a Thai construction firm in 2003 made a successful bid of 6.6 billion yen to build a drain tunnel in Bangkok, the Asahi reported.

But Nishimatsu and the Thai contractor each paid 200 million yen to the former senior official aiming to land the contract, it said.

Officials of Nishimatsu Construction were not immediately available for comment, while a spokesman for the Tokyo prosecutors office said he had no information on the reported case.

Japan has taken an increasingly hard line against corruption overseas.

Last month, Japan suspended loans to Vietnam, to which is is the largest donor, after former executives of Tokyo-based Pacific Consultants International admitted bribing a senior Vietnamese official. -- AFP