On Monday, a day after announcing a review of the original December 10-22 launch schedule, the Korean Committee of Space Technology said it was extending the window to December 29.
In a statement carried by the official Korean Central News Agency, the committee said scientists and technicians were still "pushing forward" with preparations for the mission.
"They, however, found a technical deficiency in the first-stage control engine module of the rocket... and decided to extend the launch period," it said.
North Korea says the rocket launch is a peaceful mission aimed at putting a satellite into orbit.
But the United States, Japan and South Korea say the launch is a disguised ballistic missile test, banned under UN resolutions prompted by the North's nuclear tests in 2006 and 2009.
Japan is threatening to shoot down any rocket debris that may threaten its territory.
The window extension appears to tally with South Korean media reports, citing government analysis of fresh satellite imagery, that North Korea is replacing a faulty component in the Unha-3 rocket.
In a separate report on Monday, the Chosun Ilbo - known for its comprehensive North Korean coverage - said a group of Iranian missile experts was in North Korea offering technical assistance for the planned launch.
The Iranians were invited after Pyongyang's last long-range rocket launch in April ended in failure, the newspaper said, citing a Seoul government official.