SEOUL - The operation of South Korea's oldest nuclear reactor was halted Tuesday night due to an electrical problem, a state nuclear power company said Wednesday, amid controversy over its lifespan extension.

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The Korea Hydro & Nuclear Power Co (KHNP) said the Gori 1 nuclear reactor located in the country's second largest city of Busan was turned off at about 8:46 pm local time on Tuesday after experiencing a malfunction of electricity supply.

However, the company said it was only a minor problem and that does not pose any harm to the safety of the nuclear reactor. It added that the reactor will resume its operation soon after an investigation by the state Nuclear Safety Commission.

The 587,000-kilowatt Gori 1 reactor is the oldest of 21 reactors in the country. It came into commercial operation in April 1979 and was shut down in June 2007 as it reached its initial lifespan of 30 years. The South Korean government, however, decided to run the reactor for 10 more years as it satisfied all the technical and safety standards.