Japan puts military on alert over North Korean satellite launch plans

North Korean authorities say they intend to launch an "earth observation satellite" later this month

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South Koreans watch a TV news program with a file footage about North Korea's rocket launch plans, at Seoul Railway Station in Seoul, South Korea. Image: Ahn Young-joon / AP/Press Association Images

Japan has put its military on alert over North Korean plans for a satellite launch, which are being viewed in the region as a long-range missile test.

South Korea has warned Pyongyang would pay a "severe price" if it went ahead with the move, while China has also raised concerns and called on the regime to exercise restraint.

Reports of the planned launch led to renewed calls by the US for tougher UN sanctions, which already being discussed following North Korea's recent nuclear test.

Pyongyang informed UN agencies this week that it planned to launch an "earth observation satellite" later this month.

Japan has said it will shoot down the missile if it crosses into its airspace and prime minister Shinzo Abe condemned called the plan a "serious provocation".

In a statement, the government in Seoul said: "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.

"We strongly warn that the North will pay a severe price ...if it goes ahead with the long-range missile launch plan."

US State Department spokesman John Kirby said the UN needed to "send the North Koreans a swift, firm message".

However, Pyongyang has said it has a sovereign right to pursue a space programme by launching rockets.

US officials said last week North Korea was believed to be preparing 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 what it described as a communications satellite into orbit.

Last month, North Korea claimed it had successfully tested a hydrogen bomb although doubt was cast on this by the US and South Korean officials.

They said the blast was too small for it to have been a full-fledged hydrogen bomb.