By Kim Eun-jung
SEOUL, Dec. 11 (Yonhap) -- North Korea's decision to extend its rocket liftoff deadline is believed to be connected with defects in the direction control system of the first-stage of the long-range rocket, a senior official in Seoul said Tuesday.

   The North's state media said Monday it will extend the 13-day window by one week until Dec. 29 to fix a "technical deficiency" in the first-stage control engine module of the rocket, with all three stages currently installed on a launch site in the nation's northwestern region.

   "The engine module cited by North Korea as the site of the technical deficiency indicates the rocket's first-stage direction control system," the source said, on the condition of anonymity. "(The Seoul government) assumes that the defects took place in the direction control system."

   North Korean scientists and technicians are believed to have found the glitches while systematically conducting inspections of all systems, the source said, noting the driving system needs a wing control motor to make the booster fly toward the intended direction.

   The Unha-3 rocket is an improved version of the Taepodong-2 multistage ballistic missile launched by the communist state from Musudan-ri in its northeast in April 2009. Its first stage is fitted with four booster engines of the Nodong shorter-range ballistic missile, based on the technology of Russia's SS-N-6 intermediate missile.

   "It would be hard to control (the rocket), which uses four Nodong-B missile booster engines as a propellant," the source said.

   Images taken by South Korea's commercial satellite showed several vehicles near the Dongchang-ri launch site as of Monday, Seoul officials said, interpreting it to mean work was under way to fix the problems with the rocket.

   A tower crane is still set up at the 50-meter launch pad, with a camouflage net covering the rocket, the image showed.

   As repair work is currently under way and the North's northwestern region near the launch site is forecast to have snow and rain over the weekend, it would be hard to fire off a rocket within this week, officials noted.

   In April, Pyongyang launched a similar rocket but it exploded shortly after liftoff.

   ejkim@yna.co.kr
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