Japan has deployed missile batteries in Tokyo and dispatched destroyers carrying interceptor missiles as it boosts its defences against a planned North Korean rocket launch this month.

Pyongyang says it will launch a satellite for peaceful scientific research between April 12 and 16 to mark the 100th anniversary on April 15 of the birth of founding leader Kim Il-Sung, AFP reported.

But the United States and its allies say it is a disguised missile test and that the launch would contravene UN sanctions aimed at curbing North Korea's missile programme.

Patriot missiles were Saturday deployed at three military facilities in the greater Tokyo region and the defence ministry dispatched three Aegis destroyers carrying sea-based interceptor missiles, reportedly to the East China sea.

"With the latest step, it completes the deployment of PAC3," said a duty officer at the defence ministry, referring to the Patriot missiles.

Japanese Prime Minister Yoshihiko Noda has given the green light to shoot down the North Korean rocket if it threatens Japan's territory.

In 2009, Japan also ordered missile defence preparations before Pyongyang's last long-range rocket launch which brought UN Security Council condemnation and tightened sanctions against the isolated communist state.