By Jack Kim and Nobuhiro Kubo
Japan has put its military on alert to shoot down any North Korean rocket that threatens it, while South Korea warns the North it would pay a "severe price" if it goes ahead with a satellite launch that the South considers a missile test.
North notified UN agencies on Tuesday (local time) of its plan to launch what it called an "earth observation satellite" some time between February 8 and 25.
North Korea has said it has a sovereign right to pursue a space program by launching rockets, although the US and other governments suspect that such launches are in reality tests of its missiles.
"We have defences ready to deal with all threats, but in view of the announcement I have put the Self Defence Force's Aegis destroyers and our PAC-3 units on alert and issued an order to shoot down any ballistic missile threat," Japan's defence minister Gen Nakatani told a media briefing.
Japanese Prime Minister Shinzo Abe said he would work with the US and others to "strongly demand" that North Korea refrain from what he described as a planned missile launch.
Tension rose in East Asia last month after North Korea's fourth nuclear test, this time of what it said was a hydrogen bomb.
A rocket launch coming so soon after the nuclear test would raise concern that North Korea plans to fit nuclear warheads on its missiles, giving it the capability to launch a strike against South Korea, Japan and possibly targets as far away as the US West Coast.
South Korea said the North should immediately call off the launch, which is a violation of UN Security Council resolutions, the South's presidential Blue House said in a statement.
"North Korea's notice of the plan to launch a long-range missile, coming at a time when there is a discussion for Security Council sanctions on its fourth nuclear test, is a direct challenge to the international community," the Blue House said.
"We strongly warn that the North will pay a severe price ... if it goes ahead with the long-range missile launch plan," it said.
China, under US pressure to use its influence to rein in the isolated North, said North Korea's right to space exploration was restricted under UN resolutions.
China is North Korea's sole main ally though China disapproves of its nuclear program.
"We are extremely concerned about this," Chinese Foreign Ministry spokesman Lu Kang told a briefing.
"In the present situation, we hope North Korea exercises restraint on the issue of launching satellites, acts cautiously and does not take any escalatory steps that may further raise tensions on the Korean Peninsula."
Russia's foreign ministry said on Wednesday it was deeply concerned about North Korea's decision to go ahead with a satellite launch.
"We must state that ... the North Korean side demonstrates an outrageous disregard for the universally recognised norms of international law," the ministry said in a statement.
Reports of the planned launch drew fresh US calls for tougher UN sanctions that are already under discussion in response to North Korea's January 6 nuclear test.
State Department spokesman John Kirby said the United Nations needed to "send the North Koreans a swift, firm message".
A spokeswoman for the International Maritime Organisation, a UN agency, said the agency had been told by North Korea it planned to launch the "Kwangmyongsong" satellite.
North Korea said the launch would be conducted in the morning one day during the announced period, and notified the co-ordinates for the locations where the rocket boosters and the cover for the payload would drop.
Those locations are expected to be in the Yellow Sea off the Korean peninsula west coast and in the Pacific Ocean to the east of the Philippines, Pyongyang said.
South Korea told commercial airliners to avoid flying in areas of the rocket's possible flight path during the period.