Two anti-ballistic missile radars were found to have stopped 21 times in the past three years due to a glitch in their systems, defense ministry data showed Monday.

The data, which was submitted to Rep. Lee Chul-gyu of the ruling Saenuri Party ahead of a parliamentary audit, showed that of the two Green Pine radars stationed in South Chungcheong and North Chungcheong provinces, one had stopped 13 times in the period since July 2013, while the other had stopped eight times in the same period.

The radars, which are used as an early warning system for ballistic missiles, were out of operation for up to nine days at a time.

South Korea's military acknowledged the flaw, saying that it was caused by condensation forming inside the radars' antennae. It insisted, however, that the problem had not affected its monitoring of North Korea's missile programs, as there were other radars installed on its Aegis destroyers to carry out that work.

The Air Force has temporarily installed air conditioners on the machines to prevent moisture from condensing inside them.

"By next year, we plan to buy 'radomes' to cover the radars and permanently solve the condensation problem," said an Air Force official who spoke on the condition of anonymity. (Yonhap)