Japan gave its military the green light to shoot down any incoming North Korean rocket on Friday, with tensions high ahead of a planned launch that the United States and allies say will be an illegal missile test.

Japanese and US warships have already been deployed ahead of the April 4-8 window, when the secretive North Korea has said it will launch a communications satellite - warning that shooting it down would be seen as an act of war.

But South Korea, Japan and the US have all warned the North that any launch would be unacceptable, amid fears the regime is actually intending to test a long-range missile that could reach North America.

The security council in Japan decided ahead of time to shoot down any incoming missile that could hit its territory rather than wait until a launch.

"The security council this morning decided to issue a destruction order in advance," Japanese Defence Minister Yasukazu Hamada said on Friday. "We will do our best to handle any flying object from North Korea."

North Korean said yesterday that even referring a launch to the United Nations would ruin the long-running and erratic six-nation nuclear disarmament talks, during which North Korea has already tested one missile and an atomic bomb.

US National Intelligence Director Dennis Blair said North Korea wanted to show it had the technology to launch an intercontinental ballistic missile.

North Korea is believed to be preparing to test a Taepodong-2 that could hit Alaska.

"North Korea is attempting to demonstrate an ICBM capability through a space launch," Mr Blair said.

Japan has announced no plans to strike the North Korean rocket unless it appears to pose a direct threat, for example due to a mishap that could send an errant missile or debris flying toward the country.

"There are various scenarios - for example, a case of failure," Mr Hamada said. "It's extremely unpleasant that an object flies over our territories."

Pyongyang has reportedly already put a rocket onto one of its launch pads, raising the stakes in a delicate diplomatic stand-off that has come just two months into the new US administration of President Barack Obama.

North Korean leader Kim Jong-Il reportedly suffered a stroke in August, and some analysts speculate he is trying to demonstrate he remains firmly in control of the country.

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