Japan put its military on alert on Wednesday to shoot down any North Korean rocket that threatens its territory, while South Korea warned the North it would pay a "severe price" if it goes ahead with a satellite launch that South Korea considers a missile test.
Ballistic defense units were deployed by Japan's Defense Ministry on land and sea after North Korea confirmed to UN agencies on Tuesday that it was getting ready to launch what it says it is an "earth observation satellite," sometime between February 8 and 25.
North Korea should immediately call off the planned launch, which is a violation of United Nations 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."
Japanese Prime Minister Shinzo Abe said he would work with the United States and others to "strongly demand" that North Korea refrain from what he described as a planned missile launch. State Department spokesman John Kirby said that the UN needs to "send the North Koreans a swift, firm message."
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 programme.
"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."
Reports of the planned launch drew fresh US calls for tougher UN sanctions, which are already under discussion in response to the most recent North Korean nuclear test — the country's fourth — last month. The country declared that it had successfully tested a hydrogen bomb, but this claim was met with skepticism by US and South Korean officials and nuclear experts, who said the blast was too small for it to have been a full-fledged hydrogen bomb.
Nevertheless, South Korea subsequently said that it was working with the US and allied powers to craft sanctions that would inflict "bone-numbing pain" in response to North Korea's nuclear provocations.
Pyongyang has said it has a sovereign right to pursue a space program by launching rockets, although the US and other governments worry that such launches are missile tests in disguise.
A spokeswoman for the International Maritime Organization, a UN agency, said the agency had been told by North Korea it planned to launch the 'Kwangmyongsong' satellite. The International Telecommunication Union, another UN agency, also told Reuters that North Korea had informed it on Tuesday of plans to launch a satellite with a functional duration of four years in a non-geostationary orbit.
North Korea said the launch would be conducted in the morning one day during the announced period, and notified the coordinates 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's west coast, Pyongyang said, and in the Pacific Ocean to the east of the Philippines.
US officials said last week that North Korea was believed to be making preparations for a test launch of a long-range rocket, after activity at its test site was observed by satellite.
North Korea last launched a long-range rocket in December 2012, sending an object it described as a communications satellite into orbit.