File photo - This December 4, 2012 file satellite image taken by GeoEye and annotated shows snow covering the Sohae launching station in Tongchang-ri, North Korea.

Seoul, South Korea - North Korea said on Monday that it has extended the launch period for a controversial long-range rocket by another week until December 29, citing technical problems.

An unidentified spokesman for the North's Korean Committee of Space Technology told state media that scientists found a “technical deficiency in the first-stage control engine module of the rocket.” The statement didn't elaborate but said technicians were “pushing forward” with final preparations for the launch.

The United Nations, Washington, Seoul and others call North Korean launches covers meant to test technology for missiles that could be used to strike the United States. They have warned North Korea to cancel the launch or face a new wave of sanctions.

The North Koreans called it a peaceful bid to advance its space program, and a last wish of late leader Kim Jong Il.

The North had originally set up a 13-day launch window, starting on Monday, but it announced on Sunday that it may delay the liftoff. This year's winter has seen a stretch of snowy, frigid weather.

Experts in Seoul and Tokyo had speculated that technical glitches may have forced scientists to postpone the launch of the finicky three-stage rocket, its fourth attempt since 1998.

Early Sunday, a spokesman from North Korea's Korean Committee for Space Technology told state-run media that scientists were considering “readjusting” the timing of the launch. He did not elaborate.

Temperatures in the nearby border city of Sinuiju, 50 kilometres to the north, dropped to minus-13 C (8.6 F) during the launch window, and the Korean Peninsula has been seized by early winter storms and unusually cold weather, the Korean Meterological Agency said in Seoul.

Engineers can launch a rocket when it's snowing, but lightning, strong wind and freezing temperatures have the potential to stall liftoff, said Lee Chang-jin, an aerospace professor at Seoul's Konkuk University. - Sapa-AP