TOKYO (AFP) - The operator of Japan's stricken Fukushima nuclear plant on Monday said that groundwater from an observation well near the site of a leaky storage tank showed high levels of radiation, according to reports.

The finding means that it "now seems more likely" that radioactive water from leaking tanks had mixed with groundwater in the area, Jiji press and Kyodo news agency quoted the Tokyo Electric Power Company (Tepco) as saying.

Many of the tanks were used to cool molten reactors wrecked by an earthquake and tsunami disaster in March 2011.

The well was found to have contained 3,200 becquerels per litre of beta-ray emitting materials, including strontium.

Last week, the Japanese government unveiled a half-billion dollar plan to stem the leaks by creating a wall of ice under the plant.

Tepco also plans to use wells to pump up the groundwater before it seeps into the sea.

But, according to Kyodo news, the latest findings could affect that plan as the nearest pumping well is only 130m away from the monitoring site from where the sample was taken.