Fukushima, Japan — Japan suspended operations to keep its stricken nuclear plant from melting down today after surging radiation made it too dangerous to stay.

Chief Cabinet Secretary Yukio Edano said the workers dousing the reactors in a frantic effort to cool them needed to withdraw.

“The workers cannot carry out even minimal work at the plant now,” Edano said. “Because of the radiation risk we are on standby.”

The nuclear crisis has triggered international alarm and partly overshadowed the human tragedy caused by Friday’s earthquake and tsunami, which pulverized Japan’s northeastern coastline, killing an estimated 10,000 people and severely damaging the nuclear plant.

Since then, authorities have tried frantically to avert an environmental catastrophe at the Fukushima Dai-ichi complex in northeastern Japan, 140 miles north of Tokyo.

Edano said the government expects to ask the U.S. military for help. He did not elaborate. He said the government is still considering whether and how to take up the various offers of help from other countries.

The surge in radiation was apparently the result of a Tuesday fire in the complex’s Unit 4 reactor, according to officials with Japan’s nuclear safety agency. That blast is thought to have damaged the reactor’s suppression chamber, a water-filled pipe outside the nuclear core that is part of the emergency cooling system.

Officials had originally planned use helicopters and fire trucks to spray water in a desperate effort to prevent further radiation leaks and to cool down the reactors.

“It’s not so simple that everything will be resolved by pouring in water. We are trying to avoid creating other problems,” Edano said.

“We are actually supplying water from the ground, but supplying water from above involves pumping lots of water and that involves risk. We also have to consider the safety of the helicopters above,” he said.

A U.S. nuclear expert said he feared the worst.

“It’s more of a surrender,” said David Lochbaum, a nuclear engineer who now heads the nuclear safety program for the Union of Concerned Scientists, an activist group. “It’s not like you wait 10 days and the radiation goes away. In that 10 days things are going to get worse.”

“It’s basically a sign that there’s nothing left to do but throw in the towel,” Lochbaum said.

The government has ordered some 140,000 people in the vicinity to stay indoors. A little radiation was also detected in Tokyo, triggering panic buying of food and water.

Meanwhile, a new aftershock of 6.0 magnitude rattled northeast Japan today.

Scores of strong aftershocks have followed the 9.0 magnitude earthquake that struck Friday and caused a devastating tsunami.

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