North Korea has removed a long-range rocket from its launch pad for repair, South Korean media reported Tuesday, a day after Pyongyang extended the widely-criticised mission's launch window.

According to analysis of the latest satellite imagery, the entire three-stage Unha-3 carrier has been removed to a nearby assembly facility, Yonhap news agency quoted a military source as saying.

"It seems that North Korea has pulled down the rocket from the launch pad to fix technical problems," the source said.

The defence ministry refused to confirm the report which, if true, would signal a lengthy delay in the launch schedule.

North Korea says the rocket is being used to put a satellite into orbit, but the United States and its allies insist the launch is a disguised ballistic missile test.

North Korea had originally provided a December 10-22 window for launching the rocket, but that was extended by another week on Monday when a "technical deficiency" was discovered in the first-stage engine.

Yonhap's military source said Pyongyang was expected to go ahead with a launch after repair works are completed.

The North's decision to try and launch the rocket in winter has led analysts to suggest a political imperative behind the timing, which may have overruled technical considerations.

New leader Kim Jong-Un is believed to be extremely keen that the launch falls around the first anniversary of the death of his father and former leader Kim Jong-Il on December 17.

The possibility that the launch has been rushed has been backed by missile experts, sceptical that the problem which resulted in the failure of the North's last rocket launch in April could have been resolved in just eight months.

North Korea is banned from conducting missile tests under UN resolutions triggered by Pyongyang's two nuclear tests in 2006 and 2009.

The latest planned launch has been condemned by the United Nations, as well as the United States and its main military allies in Asia, Japan and South Korea.

Russia has joined international calls for Pyongyang to cancel the mission, while China, North Korea's sole major ally and its biggest trade partner and aid provider, has expressed concern.

EU foreign ministers said Monday that an eventual launch would be a "provocative act" in breach of UN resolutions and require an international response.

UN diplomats inside and outside the Security Council have started consultations behind the scenes on what action to take if Pyongyang goes ahead with the launch.

According to Japanese reports, Japan, the United States and South Korea have agreed to demand the UN Security Council strengthen sanctions on North Korea to levels that match those on Iran.

That would include increasing the list of financial institutions, entities and individuals already subject to asset freezes.