Increased levels of the radioactive element tritium have been found in groundwater at the wrecked Fukushima nuclear plant in Japan.
Readings, taken from samples drawn from a well close to storage tanks holding contaminated water, were more than 50 percent higher on Wednesday than a day earlier.
Tritium is less harmful to humans than cesium and strontium.
Operator Tepco revealed the findings as Prime Minister Shinzo Abe and his government tried to reassure the international community that the situation at Fukushima is “under control.”
Two-and-a-half years after a massive earthquake and tsunami crippled the plant, Tepco is still struggling to pump out and treat massive amounts of contaminated water, which is rising at a rate of 400 tonnes a day.
Nuclear plants in Japan are allowed to release water with up to 60,000 becquerels of tritium per litre.
A becquerel is a measure of the release of radioactive energy.
The groundwater measurements rose to 97,000 becquerels per litre on Wednesday from 64,000 on Tuesday.