After years of tough negotiations, Japan and the 15-nation European Union have reached a basic agreement on a landmark treaty aimed at promoting cooperation in the peaceful use of nuclear energy.

Government sources said Tuesday the basic agreement will be reaffirmed and welcomed at a regular meeting of top Japanese and EU leaders planned for mid-December in Brussels.

The Japan-EU summit, if held, would be the first in 17 months, and would be attended by Prime Minister Junichiro Koizumi, Belgian Prime Minister Guy Verhofstadt and European Commission President Romano Prodi.

Belgium holds the rotating six-month EU presidency during the second half of this year. The European Commission is the EU's executive arm, which is also located in the Belgian capital.

It remains uncertain, however, whether the Japan-EU summit will actually take place in mid-December due to Koizumi's tight domestic schedule, the sources said.

According to the sources, Japan hopes to initial the nuclear energy treaty by the end of this year, formally sign it early next year and get it ratified by the Diet before late June, near the end of a 150-day ordinary session to be convened in January.

Japan and the EU opened full-scale negotiations on the nuclear energy treaty in early 1999.

At the last Japan-EU summit in Tokyo, in July 2000, then Prime Minister Yoshiro Mori, French President Jacques Chirac and European Commission President Prodi agreed to seek an early conclusion of the bilateral nuclear energy treaty.

The treaty, to be signed by the Japanese government and Euratom, the EU's organ in charge of nuclear energy, will promote bilateral cooperation in using nuclear energy for peaceful purposes and ban the conversion of fissionable materials for military use or the transfer of such materials to third-party countries.

Japan has so far concluded similar treaties with several countries, including the United States, Canada, Britain, France and Australia. Under these separate bilateral treaties, Japan purchases uranium from the U.S., Canada and Australia, while commissioning Britain and France to reprocess spent nuclear fuel.

In addition to Britain and France, Belgium and the Netherlands are commissioned to reprocess spent Japanese nuclear fuel. But Japan does not have nuclear treaties with Belgium and the Netherlands. Therefore, Japan must conclude a special administrative arrangement with Belgium and the Netherlands each time reprocessing of spent nuclear fuel is commissioned.

The Japan-EU nuclear energy treaty is expected to make it possible for Japan to cooperate more smoothly with Belgium and the Netherlands in the peaceful use of nuclear energy by saving the three countries time and administrative costs.

It was not immediately known, however, if and how the Japan-EU nuclear energy treaty might affect two existing treaties Japan has separately signed with Britain and France, both key members of the EU.