South Korea has idled two nuclear power plants after finding test results for crucial control cables were falsified.

South Korea's trade and energy ministry said Tuesday a private company fabricated the results after the cables failed international tests of their ability to withstand changes in voltage and pressure.

The cables are responsible for shutting off radioactive materials or cooling nuclear fuel during an emergency.

Another four nuclear reactors that were either shut down for scheduled maintenance or under construction were also using cables that had failed the tests.

The revelations add to worries about nuclear safety and power shortages during the summer. They are a new blow to South Korea's ambitions to export nuclear technology.

South Korea has 23 nuclear power plants which supply about 30 percent of its energy.