Japan will have to shoulder more than 1 trillion yen to help build and operate the International Space Station, a figure much higher than previously cited by the government, internal documents from the science ministry obtained by Kyodo News showed Saturday.

The increased cost estimate was briefly noted during a meeting of the government's Space Activities Commission, according to government officials, but the government has never officially said the space station project could cost Japan more than 1 trillion yen.

Kyodo News obtained the documents by requesting them from the Ministry of Education, Culture, Sports, Science and Technology under information disclosure rules.

The revelation could compel government officials to explain to the public the sharp difference from the previous official estimate, which put Japan's share of the cost at 320 billion yen, part of the total construction cost of 4 trillion yen.

Sixteen countries, including the United States, Russia and European nations, are working on the construction of the space station. Work started in 1998 some 400 km above Earth and the ISS is scheduled to be completed in 2008.

Japan is participating by building the experimental module "Kibo" (Hope), which will dock with the ISS.

According to the documents, including long-term funding plans, Japan's costs related to ISS construction and preparations for its operation total 680.7 billion yen.

Japan has so far budgeted a total of 579 billion yen from fiscal 1987 to 2003, with an additional 101.7 billion yen through fiscal 2008. The total cost includes 332.4 billion yen for constructing the module and 172.5 billion yen for ground facilities.

The government also estimates annual operating costs of 400 billion yen for some 10 years following the completion of the ISS.