Japan's nuclear regulator says radioactive water from the crippled Fukushima power plant is probably leaking into the Pacific Ocean, a problem long suspected by experts but denied by the plant's operator.
Officials from the Nuclear Regulation Authority said a leak is "strongly suspected" and urged plant operator Tokyo Electric Power Co. (TEPCO) to determine where the water may be leaking from and assess the environmental and other risks, including the impact on the food chain.
"Contamination was at its peak at the time of the accident, but I think it is continuing even after that, through the two years," said the head of the Authority, Shunichi Tanaka.
The watchdog's findings underscore TEPCO's delayed response in dealing with a problem that experts have long said existed.
On Wednesday, the company continued to raise doubts about whether a leak exists.
A TEPCO spokesman said the increase in cesium levels in monitoring well water samples does not necessarily mean contaminated water from the plant is leaking to the ocean.
TEPCO was running another test on water samples and suspects earlier spikes might have been caused by cesium-laced dust slipping into the samples, he said.
But he said TEPCO is open to the Nuclear Regulation Authority's suggestions to take safety steps.
The watchdog said Wednesday it would form a panel of experts to look into ways to contain the problem.
Tanaka said what is most important is to minimise the leak to the outside and reduce the impact on the human society, but he warned there is no silver bullet.
"It is hard to know what measure would be a rock solid solution. If there was one, we could go ahead with it, but we are not in that situation. So there could be some trial-and-error methods. But regardless, and I repeat, the direction we are heading is that we do everything we can to avoid any leakage," he said.
The Fukushima Dai-ichi plant was ravaged by the March 2011 earthquake and tsunami, and TEPCO has used massive amounts of water to cool the damaged reactors since then.
Repeated leaks of the contaminated water stored on site have hampered decommissioning efforts.
Marine biologists have warned that the radioactive water may be leaking continuously into the sea from underground, citing high radioactivity in fish samples taken near the plant.
Since May, TEPCO has reported spikes in cesium levels in underground water collected from a coastal observation pit, while the water-soluble element strontium showed high levels in seawater samples taken in areas just off the coast of the plant.
The company says most of the contamination has been there since the 2011 accident.
TEPCO has said it has detected "no significant impact" on the environment.
It says cesium tends to be absorbed in the soil, and denies water contaminated with that element reached the sea.
But the Nuclear Regulation Authority said Wednesday that samples from both the pit water and coastal seawater indicated that contaminated underground water likely had reached the sea.
Most fish and seafood from along the Fukushima coast are barred from the domestic market and from being exported.
Seafood caught north and south of Fukushima are regularly tested for radiation to make sure they are safe for consumption.
In the wider ocean, the contaminated water becomes too diluted to be harmful.
At a port located about 70 kilometres (43 miles) away from Fukushima, fishermen are concerned that leakage could affect the fishing industry.
"Personally speaking, it's a problem because if there's leakage, the seawater would be polluted and my business would be negatively affected," said one local fisherman on Wednesday.
"With this information out, I'm worried that the prices will fall because of harmful rumours," said another.
TEPCO says it has taken steps to prevent seawater contamination but that it is impossible to completely prevent the contamination from spreading.