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International nuclear regulators warned Tuesday that growing amounts of radioactive water in and around Japan’s tsunami-stricken Fukushima Daichi nuclear power plant remained a threat and said it must be disposed of responsibly.

"The situation ... remains very complex, with the increasing amount of contaminated water posing a short-term challenge that must be resolved in a sustainable manner," according to a report by the International Atomic Energy Agency (IAEA) released Tuesday. Storing and disposing of the huge amounts of contaminated water used to cool and decommission the reactors has proved an enormous challenge for the plant's administrator, Tokyo Electric Power Co (TEPCO), which has been criticized in the past for leaks and other missteps.

In addition to tainted water, the plant's administrators still have to dispose of dangerous radioactive fuel, according to the report.

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"The need to remove highly radioactive spent fuel, including damaged fuel and fuel debris, from the reactors that suffered meltdowns poses a huge long-term challenge," the statement added.

This is the third review of the Japan's plans to decommission the plant, which suffered a meltdown at three reactors after a 9.0 magnitude earthquake off the coast on March 11, 2011, triggered a massive tsunami that killed thousands and devastated parts of coastal Japan.

The 15-person IAEA team also praised Japan for trying to reduce radioactive risk and decommissioning.

"Japan has made significant progress since our previous missions. The situation on the site has improved — progressive clean-up has led to reduced radiation dose levels in many parts of the site," team leader Juan Carlos Lentijo, IAEA Director of Nuclear Fuel Cycle and Waste Technology, said in the statement.

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— F. Brinley Bruton