Japan placed its military on alert on Wednesday to shoot down a North Korean rocket if it threatens Japan, while South Korea warned the North that it will pay a "severe price" if it proceeds with a satellite launch that Seoul considers a missile test.
North Korea should immediately call off the planned launch, which is a violation of UN Security Council resolutions, the South's presidential Blue House said in a statement.
Japan military ordered ballistic missile defense units including Aegis destroyers in the Sea of Japan and Patriot missile batteries to be ready to shoot down any North Korean rocket that makes a threat, said Japan's Defense Minister Gen Nakatani said in a statement.
South Korea and Japan urged North Korea on Wednesday to stop its controversial plan to test launch a long-range missile.
Furthermore, South Korea announced North Korea's previous launch of a satellite that was a step towards launching the long-range missile and added Pyongyang would pay a "severe price" if it continues.
On Jan 6, North Korea said that it tested a hydrogen bomb, although the United States and other governments and experts voiced scepticism that it had made such a technological advance.
"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.
North Korea last conducted a long-range rocket launch in late 2012, putting into orbit an object it claimed was a communications satellite, in what experts saw as part of an effort to build an intercontinental ballistic missile (ICBM).