South Korea said Monday that it had shut down operations at two nuclear reactors after discovering that they were using parts supplied with forged quality certificates.

Halting the reactors to replace the parts will result in "an unprecedented level" of strain on the nation's power supply as it heads into the winter months, the Ministry of Knowledge Economy said in a statement.

The controversy over the products used in the Korean reactors comes amid increased scrutiny of nuclear power worldwide following the crisis at the Fukushima Daiichi nuclear plant in Japan during the aftermath of the earthquake and tsunami that hit the country in March 2011.

The unverified parts in South Korea are products like fuses and power switches that don't pose a risk of causing a radiation leak, authorities said.