The launch of South Korea's KSLV-1, its first space launch vehicle, which was due to take place on Friday morning, has been put off owing to a minor failure in its Russian-made Khrunichev RD-191 first-stage rocket motor, the Russian space agency said.

"During preparation for launch, a problem was detected in the first-stage system," a Roscosmos spokeswoman told Kommersant daily. "A decision was made to take the rocket off the launch pad, take it to a test platform and make additional checks," she said.

"A leak has been detected from a connection between the first-stage rocket of the KSLV-1 and the launch pad," Korea's Science and Technology Minister Cho Yul-rei told Yonhap news agency.

Cho said the leak had been detected a few hours before the launch time when helium was injected into the rocket to check its integrity. The launch will have to be delayed by at least three days, he added.

Russian experts later confirmed a seal in the coupling device that connects the rocket to the launch pad had broken, Yonhap said.

The rocket launch, from the Naro space center around 300 miles south of Seoul, was the third attempt at a KSLV launch after two others failed in 2009 and 2010.