Sweden's nuclear energy capacity was cut to half after authorities shut down five of the country's reactors, four of them in connection with a potentially dangerous failure caused by an electricity blackout at a nuclear power plant last week.

The fifth reactor has been closed down for routine maintenance.

The Swedish Nuclear Power Inspectorate (SKI) said Friday it was satisfied that the remaining five reactors still in operation were not affected by the same problem that led to a blackout at the Forsmark nuclear power station on the east coast, amid allegations that a potentially catastrophic reactor meltdown had been avoided by sheer luck.

"We will allow the reactors that are running to continue running," SKI spokesman Anders Bredfell told AFP.

No decision had been taken about the reactors that were not currently operating, he said.

"We will take the time we need to make sure that safety comes first," he said.

SKI told AFP it was treating the Forsmark blackout as a level two incident on a scale from zero to seven.

Sweden has shut two of its original 12 nuclear reactors since 1999 as part of a plan to phase out nuclear power over the next 30 or so years, or when the reactors' lifespan expires.

Nuclear power accounts for nearly half of Sweden's electricity production.

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