By YUKA HAYASHI And ANDREW MONAHAN

TOKYO—Japanese officials continued their battle to control dangerous reactor overheating in the nation's worst nuclear accident that followed Friday's earthquake, as they resorted to an unprecedented attempt to cool the reactor with seawater.

Reuters

Official in protective gear scans for signs of radiation on a man who is from the evacuation area near the Fukushima Daini nuclear plant in Koriyama on Saturday.

Japan Chief Government Spokesman Yukio Edano said Sunday that work is continuing on attempts to shut down two nuclear reactors at Tokyo Electric Power Co.'s Fukushima Daiichi power plant in northern Japan.

Mr. Edano acknowledged that radiation levels have risen at the plant as venting of slightly radioactive steam continues in a bid to lower pressure in the container vessel and allow the pumping of cooling water.

"The rise in the radiation levels was within the expected range as we continue venting," he said Sunday.

The radiation being released by the venting is minimal, he added. Officials at Tokyo Electric, which operates the plant, earlier said levels had exceeded the legal limit, a disclosure that is required under law.

Mr. Edano said fluctuations in the radiation level can be expected, and that there are no health concerns.

"We can expect to see more fluctuations in the radiation levels as we continue venting the No. 1 and No. 3 reactors," he said.

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