The level of radioactive iodine-131 found in seawater near the troubled Fukushima Daiichi nuclear power plant, 240 kilometers northeast from Tokyo, has soared to its highest reading yet at a concentration of 4,385 times the legal limit.

Pressure has been mounting for Japanese authorities to expand the 20-kilometer evacuation zone around the stricken six-reactor facility following the continuous leaking of radiation since the March 11 magnitude-9.0 earthquake and tsunami knocked out the plant's critical cooling systems.

The level of iodine-131, reported a few hundred meters south of the facility's southern water outlet, has surged drastically in a series of tests since last week, carried out by beleaguered plant owner and operator Tokyo Electric Power Co. (TEPCO).

Previous readings there showed concentration levels at 1,250 times the legal maximum on Friday, 1,850 times the limit on Saturday and 3,355 times the limit on Tuesday.

A spokesperson for TEPCO said on Thursday the massive spike in radioactive iodine in seawater has been caused by water that has been in contact with nuclear fuel or reactors, but said the means of the contaminated water flowing into the Pacific Ocean were, as yet, unknown.

Deputy Director-General of Japan's Nuclear and Industrial Safety Agency Hidehiko Nishiyama conceded Thursday that radioactive materials have and continue to be freely leaking into the sea. "We must check that possibility well," said Nishiyama.

Nishiyama said once again that human health in the area was not at imminent risk, although failed to comment on the possible long- term affects of exposure to the radiation in the area.

He also said that as no fishing was being conducted in the area marine life would not be significantly affected, adding that any radioactivity in fish would dissipate before being consumed by people.

But Japan's nuclear safety agency, in light of the new readings and concerns of international nuclear watchdogs, will add three new offshore monitoring stations, to better gauge the rising level of radioactive seawater in the area.

Thursday's massive spike in radiation has caused concern to the International Atomic Energy Agency (IAEA), who has insisted Japan increase its radiation monitoring activities and expand the evacuation zone around the radiation-leaking facility.

Speaking at a news conference Thursday Chief Cabinet Secretary Yuikio Edano said that the central government had heeded the advice of the U.N. nuclear watchdog and will boost radiation checks and expand the evacuation zone, when deemed necessary.

"We have no plans to immediately evacuate people, but naturally, high radiation levels in soil, if continued over a long period of time will likely affect human health, so we need to step up our monitoring, and if need be, take steps to deal with it," Japan's top government spokesperson said.

The IAEA said Thursday that the concentration of radiation found in soil samples taken 40 km from the plant, 20 km further than the current evacuation zone, were of levels exceeding the agency's standards.

But whilst the authorities refuted claims that the situation posed an immediate threat to human health, the Japanese government said it plans to redouble its radiation data monitoring around the plant, located on the Pacific coast 240 km northeast of Tokyo.

The No. 1, No. 2 and No. 3 reactors at the stricken power plant have suffered massive damage to their cores, causing them to release radioactive substances and the nuclear fuel rods of the No. 4 reactor kept in a spent fuel pool are believed to have been exposed directly to the atmosphere at one point, following damage sustained after the earthquake and tsunami.

The utility firm's efforts to cool the overheating reactors with seawater likely led to some of the reactor buildings being flooded and contaminated water leaking into drainage and electrical trenches at the plant.

Two TEPCO workers were hospitalized with serious burns caused by beta rays having been soaked in knee-high radioactive water due to not wearing protective boots or waterproof hazmat suits.

To date, 19 TEPCO employees have been exposed to levels of radiation that exceed legal limits and are considered to be harmful to health.

In a desperate bid to minimize radioactive particles being released from the plant into the atmosphere, TEPCO planned to spray a water-soluble resin onto reactors Thursday, but the test was postponed due to rain.

When the weather clears TEPCO will begin by spraying the south and west sides of the No. 4 reactor with a total of 60,000 liters over a period of two weeks, according to the utility firm's provisional plans.

Whilst the government announced Wednesday that the six-reactor facility will be scrapped once the nuclear crisis has been brought under control and the four troubled reactors had effectively gone through a cold shutdown, TEPCO said the process of decommissioning the plant could take as long as two years.

In addition to spraying resin on the leaking reactor building and other contaminated materials like the immense amount of radioactive rubble at the plant as a result of the earthquake, the government was mulling taking the unprecedented measure of covering three of the badly damaged nuclear reactor buildings with special fabric caps and fitting air filters to limit radiation leakage.

The government in twine with nuclear experts is also considering sealing the troubled reactors in a concrete grave, similar to measures that were taken to curb the 1986 Chernobyl disaster.

Due to high levels of radiation in the vicinity of the plant, local authorities have been unable to collect somewhere in the region of 1,000 bodies of victims of the March 11 earthquake and tsunami from within the evacuation zone around the nuclear plant, police reports said Thursday.

The irretrievable bodies continue to be exposed to high levels of radiation day-by-day as they decompose, local police sources said.