Fueling of the rocket, which North Korea says will put a satellite in orbit, is under way and will be completed at the "appropriate time," said Paek Chang Ho, head of the North Korean General Satellite Control and Command Center.
He declined to be more specific.
The announcement last month of the satellite launch -- which countries like the United States and South Korea see as a cover for a ballistic missile test -- ratcheted up tensions in the region and prompted Washington to suspend a recent deal to supply food aid to the North.
The launch of the rocket is scheduled to take place between Thursday and Monday, and countries in the region are on edge.
Japan has deployed missile defenses and says it will shoot down any part of the rocket that comes near its territory. South Korea has described the move as a "grave provocation" and says it will respond with "appropriate countermeasures."
"This launch will give credence to the view that North Korean leaders see improved relations with the outside world as a threat to the existence of their system," U.S. Secretary of State Hillary Clinton said in a speech Tuesday. "And recent history strongly suggests that additional provocations may follow."
A recent report from South Korean intelligence officials claimed that North Korea is planning a new nuclear test in the area where it staged previous atomic blasts.
The South Korean intelligence report noted that the two previous rocket launches that Pyongyang said were intended to put satellites into orbit were followed a few weeks or months later by nuclear tests.
International leaders have urged North Korea to cancel the imminent rocket launch, but Pyongyang has refused to back down, insisting that the operation is for peaceful purposes.
The last time Pyongyang carried out what it described as a satellite launch, in April 2009, the U.N. Security Council condemned the action and demanded that it not be repeated.
The announcement of the fueling of the rocket comes on the same day as a conference of the North Korean ruling Workers' Party that is expected to cement the position of the secretive state's new leader.
The meeting of party delegates and the controversial launch come as the nation prepares to mark the 100th anniversary of the birth of Kim Il Sung, the founder of North Korea who ruled the Communist state for more than four decades. His birthday on April 15, known as the "Day of the Sun," is a key public holiday in the North Korean calendar.
At the conference, Kim Il Sung's grandson, Kim Jong Un, is likely to be named secretary-general of the Workers' Party, a key post that would underline his status as "supreme leader" of the insular regime, according to Chung-In Moon, professor of political science at Yonsei University in Seoul.
That appointment would be "a very important signal that he's consolidating power and positions from an institutional point of view," Moon said last week.
It would also mean that Kim Jong Un would become chairman of the party's central military committee, following in the footsteps of his father, Kim Jong Il, who died in December.
Kim Jong Un is already described as the "supreme leader" of the party, state and army.
Moon noted that it is still unclear how directly the young Kim, thought to be in his late 20s, is involved in policy decisions.
So far, Kim Jong Un, as the direct descendant of the country's founder, appears to be "reigning," while powerful senior officials in the regime like his uncle, Jang Song Taek, seem to be doing the "ruling," Moon said.
