Activity around the site at Musudanri has been brisk over the past month, they said, but there is no sign that fuel injection had started.

"North Korea has not yet reached the final stage of preparations to fire it. It has not yet started fuel injection," said Baek Seung-Joo from the government-backed Korean Institute for Defence Analyses.

"It will take at least two days to fill the rocket with liquid fuel and if they finish it, we can say they are ready to start the countdown," he told AFP.

Officials here and in Washington confirmed earlier this week that North Korea appeared to be preparing to launch an inter-continental ballistic missile capable of reaching the mainland United States.

Experts describe rocket fueling as the point of no return for a launch, because the process is both difficult and dangerous to reverse.

South Korea has urged Pyongyang to abandon plans for the missile test that would have a "negative impact on the international geopolitical situation and the settlement of North Korea's nuclear issue."

A top official of the presidential Blue House said Thursday that the warning had been based on the government's judgement that North Korea might test-fire a missile but said the "explicit movement" for such a move had not begun.

An unidentified military intelligence official was quoted as saying in a news report Friday that a long trailer, usually used to carry missiles, was spotted in the area but that there were "no signs of trucks carrying fuel."

Satellite pictures showed North Korea had set up part of a launch pad at Musudanri, the Kyonghyang daily newspaper said.

The communist regime, which is boycotting nuclear disarmament talks, could be preparing to fire a 35-meter (116-foot) Taepodong-2 in the range of 3,500 to 6,000 kilometers (2,200 to 3,750 miles), Japanese officials said.

North Korea is believed to be developing the missile for a range of up to 10,000 kilometers, which would put the continental United States within striking distance.

"It is one thing for the North to prepare for firing a missile and it is another thing for it to actually do it as the costs for firing the missile will be simply too great for the North to bear," Baek said.

He said North Korea would face international condemnation and sanctions and South Korea would come under pressure to end its policy of reconciliation towards the communist state. Japan would intensify efforts to build a missile defence system, he added.

North Korea shocked the world in August 1998 by firing a long-range Taepodong-1 missile with a range of up to 2,000 kilometers over Japan into the Pacific Ocean, claiming it was a satellite launch.

Baek recalled that North Korea also appeared to be make feverish preparations to test a long-range missile in September 2004, with military troops, vehicles and engineers swarming around the same site.

The expected test-firing never took place and North Korea later accused Washington of spreading false rumours.

Japan on Thursday downplayed the possibility of an imminent missile test after its ally the United States warned of a response if Pyongyang carried out a long-range launch.

"We are not in an extremely serious situation," Japanese Foreign Minister Taro Aso said.

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