Japan nuclear: Radiation halts water clean-up
Operators of Japan's Fukushima nuclear plant have suspended an operation to clean contaminated water hours after it began due to a rapid rise in radiation.
Some 110,000 tonnes of water have built up during efforts to cool reactors hit by the 11 March earthquake and tsunami.
The contaminated water, enough to fill 40 Olympic-sized swimming pools, has been at risk of spilling into the sea.
The disaster caused meltdown at three of the reactors, and radiation leaks.
It is the world's worst nuclear accident since Chernobyl in Ukraine in 1986.
The powerful earthquake and the tsunami it generated are now known to have killed more than 15,280 people, while nearly 8,500 remain unaccounted for.
A spokesman for the plant operators, the Tokyo Electric Power Company (Tepco), said engineers were trying to find the cause of the jump in radiation levels.
"The level of radiation at a machine to absorb caesium has risen faster than our initial projections," the spokesman said.
The disaster in numbers
He added that until they knew what was causing the rising levels they would not know when the operation would be able to resume.
"But I'd say it's not something that would take weeks," he added.
Dealing with the radioactive water is a key step to bringing the crisis at the Fukushima Daiichi plant under control, reports the BBC's Roland Buerk from Tokyo.
It is the rainy season in Japan and the pools of contaminated water could overflow, adding to radiation already released into the sea, adds our correspondent.
Earlier this week, officials had warned the radioactive pools were in danger of spilling into the sea within a week.
The Fukushima power station went into meltdown after its cooling systems were crippled by March' s devastating earthquake and tsunami.
The teams at the plant suspect the radiation rise may be linked to sludge flowing into the machinery intended to absorb caesium or the pipes surrounding it.
The tsunami destroyed both power and back-up generators at the plant, breaking the cooling systems.
The three unstable reactors are supposed to be brought to "a stable and cold shutdown" by January 2012. Despite the setbacks Tepco says it is still on track to meet that deadline.