North Korea says it is to launch a long-range rocket later this month.
The launch, planned for between December 10 and December 22, has significantly increased already strained tensions with South Korea, which holds a presidential election later this month.
South Korea's Foreign Ministry reacted swiftly to the news, expressing "grave concern" and saying Pyongyang could face severe repercussions from the international community.
North Korea tried in April to launch a long-range rocket but it broke apart shortly after lift off, crash-landing in the Yellow Sea.
The country's space agency, the Korean Committee for Space Technology, said it had studied the mistakes made in the April launch and had improved the rocket.
"Scientists and technicians of the DPRK analysed the mistakes that were made during the previous April launch and deepened the work of improving the reliability and precision of the satellite and carrier rocket, thereby rounding off the preparations for launch," it said.
Pyongyang claimed that the much-hyped failed April launch was intended to put a polar-orbiting earth observation satellite into orbit.
However, the US, South Korea and the UN all insisted it was a disguised ballistic missile test using a three-stage variant of the Taepodong-2 inter-continental ballistic missile.
The April test put a halt to the latest international effort to engage with North Korea, with the US calling off plans to deliver badly needed food assistance.
British Foreign Secretary William Hague condemned Saturday's announcement and urged authorities to drop the plan.
"Failure to do so must lead to a further response by the international community, and will damage the prospects for peace and stability on the Korean Peninsula," Mr Hague warned.
The announcement confirmed more than a week of speculation that a new launch was imminent.
Satellite imagery, released by DigitalGlobe, showed a marked increase in activity at a North Korean launch site.
Comparisons with earlier satellite imagery of the Sohae Satellite Launch Station near the Chinese border showed an increased number of people, trucks and other equipment.
"Given the observed level of activity ... a new tent, trucks, people and numerous portable fuel/oxidiser tanks, should North Korea desire, it could possibly conduct its fifth satellite launch event during the next three weeks," DigitalGlobe said in a statement last week accompanying its image.
Reports in Japan and the US had also suggested intelligence analysts in those countries were concerned about an increase in activity.
On Thursday, the UN Security Council had cautioned Pyongyang against going ahead with another launch, saying it would be "extremely inadvisable".
South Korea has reacted with anger to the latest launch plan, saying the "so-called rocket launch" is a long-range missile that violates a UN ban.
Voters in South Korea go to the polls on December 19. The neck-and-neck contest pits the ruling conservative party candidate Park Geun-hye, daughter of former South Korean leader Park Chung-hee, against Democratic Union Party candidate Moon Jae-in.
The policies they are expected to adopt in relation to North Korea differ markedly. Democratic candidate Mr Moon is expected to adopt a "carrot and stick" approach. Ms Park's stance is more "stick, then carrot".