TOKYO - Japanese engineers on Monday were forced to release radioactive water into the sea while resorting to desperate measures such as using bath salts to try to find the source of the leaks at a crippled nuclear power complex.

Tokyo Electric Power (TEPCO), operator of the Fukushima Daiichi nuclear plant, had to release low-level radioactive seawater that had been used to cool overheated fuel rods after it ran out of storage capacity for more highly contaminated water, Chief Cabinet Secretary Yukio Edano said.

TEPCO said it would release more than 10,000 tons of contaminated water that was about 100 times more radioactive than legal limits.

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Engineers are still struggling to regain control of damaged reactors at the plant in the worst nuclear crisis since Chernobyl in 1986, with the government urging TEPCO to act faster to stop radiation spreading.

But it could take months to stem the leaks, warned one official, and even longer to regain control of the power station, damaged by a March 11 earthquake and tsunami.

"We need to stop the spread of (contaminated water) into the ocean as soon as possible. With that strong determination, we are asking Tokyo Electric Power Co to act quickly," said Edano.

"If the current situation continues for a long time, accumulating more radioactive substances, it will have a huge impact on the ocean."

In their desperation, TEPCO engineers have used anything at hand to try to stop the leaks.

On the weekend, they mixed sawdust and newspapers with polymers and cement in an unsuccessful attempt to seal a crack in a concrete pit at reactor No 2.

On Monday, they resorted to powdered bath salts to produce a milky color to help trace the source of the radiation leak.

TEPCO said it was also planning to drape a curtain into the sea off the nuclear plant to try to prevent radioactive silt drifting out into the ocean.

The silt-blocking fence will take several days to prepare, said Hidehiko Nishiyama, deputy director-general of the Nuclear and Industrial Safety Agency (NISA).

The exact source of the radiation leaks remains a mystery, with NISA investigating a damaged embankment near a sluice gate at the No 2 reactor.

Japan may review its emission reduction pledge for 2020 as a result of the crisis at the Fukushima nuclear plant, Hideki Minamikawa, vice-minister for global environmental affairs, was quoted by the Yomiuri newspaper as telling reporters in Bangkok on Sunday.

Edano later said the government has yet to decide whether to review its goals for cutting greenhouse gases, as it still needs to understand the overall impact of the nuclear crisis and the prospects for post-quake reconstruction.

"It is true that our reduction target will be affected significantly," Minamikawa said.

Underlining the concern over the impact on the world's third largest economy, a central bank survey showed big manufacturers expected business conditions to worsen significantly in the next three months, although they were not quite as pessimistic as some analysts had expected.