The "Unha-3" rocket is expected to fly over western Japan after it is launched from a pad on North Korea’s west coast between April 14-16. That has raised concerns that a failed launch, or a falling stage of the rocket, could endanger Japanese lives or property.

"We must be fully prepared to protect the safety of our nation," Naoki Tanaka said after issuing the order at a meeting military commanders.

Officials have said Japan is likely to send three AEGIS-equipped destroyers to the Pacific and East China Sea and deploy mobile Patriot missile launchers to islands in Okinawa. An interceptor missile unit is also likely to be deployed in Tokyo, although the capital is well away from the expected flight path.

Seoul has also warned it might shoot down any parts of the North Korean rocket that pass over South Korean territory.

North Korea has said it plans to launch a satellite into orbit. Japan, the United States and other countries claim it is also seeking to test the capabilities of its long-range missiles, in violation of international agreements.

Japan mobilized its interceptor units and issued a similar warning to North Korea before a rocket launch in 2009, but did not follow through.

Interceptor missiles on the Japanese destroyers would serve as the first line of defense, and the land-based Patriot missiles would be a backup. Japan has successfully tested its interceptor missiles, but has never used them in a real-world situation.