Japan nuclear plant data error 'unacceptable'

The Tokyo Electric Power Company (Tepco) had previously said radiation levels were 10m times higher than normal before correcting the figure to 100,000 times.

The mistaken reading at the Fukushima Daiichi plant has called into question the operating company's handling of the current crisis. "Considering the fact that the monitoring of radioactivity is a major condition to ensure safety, this kind of mistake is absolutely unacceptable," government spokesman Yukio Edano told a news conference.

"(The government) has ordered Tepco not to repeat this again," he said, adding that the government understood the workers were overworked and under stress.

Tepco apologised on Sunday for the "mistake" in reporting a radiation spike 10 million times above normal.

Tepco said a worker taking the reading in a part of reactor 2's cooling system had no time to confirm with a second reading because the radiation level was so high he had had to leave the area.

"The number is not credible. We are very sorry," said Tepco spokesman Takashi Kurita.

Tepco has been criticised for a lack of transparency and failing to provide information more promptly and for making a number of mistakes, including worker clothing.

Radiation measurements from a pool of water inside Fukushima's reactor No 2 suggested its fuel rods had suffered a partial meltdown, Edano went on to say. “The radiation seems to have come from fuel rods that temporarily melted down and came in contact with the water used to cool the reactor.

"Steam may have condensed... carrying water from within the containment vessel," he said. That water is the most contaminated to be found at the plant so far.

Work is continuing to remove the contaminated water from the reactor building; the priority is to ensure that it doesn't seep out into the soil or the sea, our correspondent says.

Two workers were taken to hospital last week after wading though contaminated water with inadequate protection. They are expected to be released on Monday.

Workers are battling to stop radiation leaks at the Fukushima plant, hit by a quake and tsunami over two weeks ago.

Meanwhile, Japan has lifted a tsunami warning that was issued after another earthquake off its northern coast.

The 6.5-magnitude quake struck at 0723 local time on Monday (2223 GMT Sunday), 109km (67 miles) east of the badly-damaged port city of Sendai.

It is not reported to have caused any damage.

A 9.0-magnitude earthquake on 11 March and the powerful tsunami it triggered killed more than 10,000 people and left many thousands more missing.