Tokyo Electric Power Co. said that strontium, one of fatal radioactive substances, was found in underground water of the plant and seawater near it.

The substance, whose effect on human body is more fatal than cesium and iodine detected so far, has been found in soil in Fukushima Prefecture since mid-April.

However, this is the first time strontium was detected in groundwater and seawater, TEPCO said. Strontium measured in seawater was 240 times the normal levels.

Experts have said it proves that the radioactive contamination level in not only ground but also marine is very serious.

In another development, curium and americium were found out in the prefecture.

Curium was detected in Okuma cho located three kilometers from the plant, the Ministry of Education, Culture, Sports, Science and Technology reported, saying that it is a dangerous nuclear substance.

It was confirmed by TEPCO that the water contaminated with high level of radiation has been running into the sea.

According to its survey into seawater in around the plant, 5.6 Bq of iodine-131 per 1cc of seawater was detected at the intake of nuclear reactor No. 2, which meant 140 times the normal levels.

Radioactive substances have been found in seawater near intakes of other reactors, too.

Amid the growing radiation crisis, minute amount of cesium was detected in breast milk of some mothers with suckling residing in eight prefectures including Fukushima and Miyagi.

The damage by the killer quake and tsunami is increasing in scale.

The number of deaths totaled to 15,413 and that of those missing to 8,069 as of June 11, according to the Police Agency.

Meanwhile, 500 afterquakes with above 5 magnitude had been recorded until 08:00 of June 2 after the killer quake in March, said Tokyo Shimbun.