North Korea has said it is injecting fuel into a long-range rocket ahead of a launch condemned by its neighbours and the West.
The launch is set to take place between tomorrow and next Monday and has prompted neighbours such as the Philippines to re-route their air traffic just in case.
Japan said it will shoot down the rocket if it crosses its airspace.
The launch of the Unha-3 rocket, which North Korea says will put a weather satellite into space, breaches UN sanctions imposed to prevent Pyongyang from developing a missile that could carry a nuclear warhead.
It coincides with the 100th birthday celebrations of the founder of North Korea, Kim Il sung, whose grandson, Kim Jong-un, now rules.
"I think the fuel injection will be completed at an appropriate date," Paek Chang-ho, head of the satellite control centre of the Korean Committee of Space Technology, told foreign journalists in the North Korea capital, Pyongyang.
He would not comment on when the fuel injection would be complete. "And as for the exact timing of the launch, it will be decided by my superiors," Mr Paek said.
Regional powers said the launch is a disguised test of the North's long-range missile.
South Korea, which remains technically at war with the North after their 1950-53 conflict ended with a truce rather than a peace treaty, warned Pyongyang it would deepen its isolation if it went ahead with the launch.
Security sources in Seoul, citing satellite images, have said that North Korea is also preparing a third nuclear test following the rocket launch.
US Secretary of State Hillary Clinton warned that history pointed to "additional provocations" from North Korea after the launch, apparently a reference to a nuclear test.
"This launch will give credence to the view that North Korean leaders see improved relations with the outside world as a threat to their system," she told cadets at the US Naval Academy in Annapolis, Maryland.
"And recent history strongly suggests that additional provocations may follow."
She also called on China to do more to ensure regional stability.
China, North Korea's only major ally, yesterday reiterated its pleas for calm.
Foreign Ministry spokesman Liu Weimin told a press briefing in Beijing that China had "repeatedly expressed its concern and anxiety about the developments.”
