After suspending the launch, the Ministry of Education, Science and Technology and the Korea Aerospace Research Institute said mission control personnel removed the Korea Space Launch Vehicle-1's fuel and oxidation agent, South Korean news agency Yonhap reported.
"The automatic launch sequence automatically turned off due to a problem that was detected in the countdown," said Lee Sang-mok, deputy minister of science and technology policy.
Lee said a movable valve operated by helium did not function properly because of weak pressure inside the tank.
Lee said fuel and oxidation agents would be extracted and stored, a process that takes about three days.
"South Korean and Russian experts will carefully check the cause of the problem in the valve and decide whether to take the KSLV-1 back to the rocket assembly complex or refuel for blastoff at the launch pad,"
Lee said. "We have no experience in such matters, with the every effort being made to ensure that the rocket is checked and the cause found."
South Korea has been working with Russia to build a rocket capable to carry a satellite into orbit, Yonhap said.
The suspension marks the seventh time that the project, which started in 2002, has required Seoul to reschedule the liftoff. South Korea launched two satellites, Arirang-1 in 1999 and Arirang-2 in 2006, as part of its space partnership with Russia.