TOKYO - Japan may need an alternative plan to bring one of its tsunami-stricken nuclear reactors under control, given the slow progress in removing highly radioactive water hampering work to repair critical cooling pumps, Japan's nuclear watchdog said on Thursday.

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"It may be difficult to completely remove the contaminated water and so allow work to proceed. We may need to think of other options," said Hidehiko Nishiyama, Nuclear and Industrial Safety Agency Deputy Director-General.