Swedish nuclear authorities held an emergency meeting Thursday after two reactors were shut down at a plant in the southeast of the country.

The plant in Oskarshamn, about 150 miles south of the capital, Stockholm, shut down two of its three reactors late Wednesday after the company running the plant reported that "safety there could not be guaranteed."

The decision followed an incident last week at another nuclear plant in Sweden, in Forsmark, where backup generators malfunctioned during a power outage, forcing a shutdown of one of its reactors, said Anders Bredfell, a spokesman for the Swedish nuclear authority, SKI.

Bredfell said the reactors would remain shut until authorities determine whether the plant's backup generators could malfunction in the same way as at Forsmark.

Meanwhile, Greenpeace in Sweden asked the government to consider shutting down all reactors in the country and probe whether there may be a generic fault in their backup battery systems, the group's representative Martina Krueger said.

The environmentalist Green Party called on the government to appoint an independent commission to investigate nuclear safety.

The Oskarshamn plant supplies about 10 percent of the electricity used in Sweden. The reactors there were commissioned in 1972 and were Sweden's first commercial nuclear power unit.

Anders Osteberg, spokesman for the OKG company running the Oskarshamn plant, said the shutdown was costing it $1.39 million a day, but that it had to take that setback because its "obligation is to have highest safety measures in place."

Krueger said the incident in Forsmark, 46 miles north of Stockholm, was "serious" because it showed that a "meltdown" could easily happen.

"When the generators could not kick in for emergency cooling, authorities realized there might be a problem in the battery system and that it might be generic to all reactors in the country," Krueger said.

Forsmark supplies one sixth of Sweden's electricity.

After the shutdowns at Oskarshamn and Forsmark, five of Sweden's existing 10 nuclear reactors remained open. Another reactor at Forsmark and one at the Ringhals plant had been closed earlier for annual maintenance.

Urban Bergstrom, an analyst for the Swedish Energy Agency, said the country is unlikely to run low on energy because it relies heavily on hydropower during the summer.

But if the shutdowns stretched into winter, that could "cause big problems," he said.

In 1992, nuclear authorities shut down five reactors for several months after serious flaws were discovered in their cooling systems. The next year, seven were shut for a while because of various failures.

Sweden decided in a 1980 referendum to phase out nuclear power by 2010.