OSAKA -- Antinuclear activists in Japan warned in a letter sent Thursday to the International Atomic Energy Agency that tests at the Rokkasho, Aomori Prefecture, reprocessing plant scheduled for early next month will violate the government's policy of holding no surplus plutonium.

"The government of Japan made a written and unequivocal pledge to the IAEA in December 1997 to uphold the principle of no surplus plutonium. Despite this commitment, Japan will separate out four tons of plutonium at the Rokkasho plant if active testing using spent nuclear fuel begins in February," the letter says.

The letter was sent by the Tokyo-based Citizens' Nuclear Information Center and Greenpeace Japan, along with Kyoto-based Green Action. It calls on the IAEA Secretariat and Board of Governors to begin immediate discussions on the matter and to take "appropriate action" before active testing begins next month.

IAEA officials were not immediately available for comment for this article. However, privately, some have expressed concern about what the operation of the Rokkasho fuel reprocessing plant, scheduled to come into commercial operation in 2007, would mean for the proliferation of nuclear materials.

IAEA Director General Mohamed ElBaradei has proposed that new reprocessing facilities be placed under international control in order to ease proliferation concerns.

But the government's position is that even though Rokkasho has yet to go into operation, it is an existing facility and therefore outside the ElBaradei proposals.

Some local political leaders are also concerned about the possible proliferation risks of operating Rokkasho.

In August, Fukushima Gov. Eisaku Sato asked the Atomic Energy Commission why Rokkasho was necessary when the government has yet to determine how the roughly 43 tons of plutonium it already possesses would be disposed of.