A ministry spokesman said on Tuesday the tour might start on 14 January and could include South Korea.

This is the latest move in a tug-of-war between the European Union and Japan, both of which are bidding for the International Thermonuclear Experimental Reactor (ITER).

The European Union is backing Cadarache in southern France, while Tokyo is pushing Rokkasho, a remote fishing village in northern Japan, as its proposed site for the world's first attempt at generating energy in the same way as the sun.

At a meeting in Washington on 20 December, the six members of the ITER joint venture failed to reach an agreement, with the United States and South Korea backing Japan, while Russia and China favoured France.

Media reports have suggested that the deadlock over the multi-billion dollar project reflected Washington's displeasure over France's opposition to the US-led war in Iraq.

The six countries are set to meet again next month.

Compromise

France has proposed a compromise whereby the reactor would be in Cadarache, but data analysis could take place elsewhere.

Nuclear fusion has been touted as a solution to the world's energy problems, as it would be low in pollution and would theoretically use seawater as fuel.

Fusion involves sticking atoms together, as opposed to today's nuclear reactors and weapons, which produce energy by blowing atoms apart.

Fifty years of research, however, have failed to produce a commercially viable fusion reactor.