TOKYO — A crisis over contaminated water at Japan’s stricken nuclear plant worsened Saturday when the plant’s operator said it detected high radiation levels near storage tanks, a finding that raised the possibility of additional leaks.

The operator, Tokyo Electric Power Co., or TEPCO, said it found the high levels of radiation at four separate spots on the ground near some of the hundreds of tanks used to store toxic water produced by makeshift efforts to cool the Fukushima Daiichi plant’s three damaged reactors.

The highest reading was 1,800 millisieverts per hour, or enough to give a lethal dose in about four hours, TEPCO said.

The contaminated spots were found as TEPCO employees checked the integrity of the tanks after a leak two weeks ago that released 300 tons of toxic water into the Pacific.

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That leak prompted Prime Minister Shinzo Abe to announce that the government would step in to help get the plant under control, amid rising public fears of a second environmental disaster at the plant crippled two years ago by an earthquake and tsunami.

Saturday’s discoveries suggested there may have been other leaks from the tanks, many of which appear to have been shoddily built as TEPCO has scrambled to find enough storage space for the contaminated water being produced by the plant.

However, TEPCO said it had found no evidence of fallen water levels in nearby tanks, making it unclear how much water, if any, may have leaked out, and whether any reached the Pacific, about 1,500 feet away.

About 430,000 tons of contaminated water, enough to fill 170 Olympic-size pools, is stored in rows of tanks at the plant, which appears to be running out of open space to put them all.

The contaminated water increases by 400 tons every day as groundwater flows into the basements of the damaged buildings housing the three ruined reactors, which melted down in the worst nuclear accident since Chernobyl in 1986.

TEPCO must draw off that water to prevent it from overwhelming jury-rigged cooling systems.