Tokyo is considering deploying both its ballistic missile interceptor warships to the Sea of Japan ahead of a possible test launch of North Korea's longest-range missile, Kyodo news agency reported on Tuesday.

The U.S. military is closely monitoring activities in North Korea from its bases in Japan, officials said Tuesday.

The North said last week that it would launch a communications satellite into orbit. But neighboring governments believe the satellite claim may be a cover for a missile launch and have warned the regime not to carry out any "provocative" actions.

Japanese Prime Minister Taro Aso indicated earlier this week that Japan should be able to use its missile defence capabilities even if North Korea insists that it is launching a satellite, domestic media reported.

Failure to shoot down a target could undermine faith in Japan's defence system, which was introduced with U.S. help after North Korea fired a missile over the country in 1998, stunning the region.

Analysts say satellite images reveal brisk activity at a launch pad in North Korea's northeast.

U.S. military officials at Misawa Air Base, which is on Japan's northern fringe just across the Sea of Japan from North Korea, said they are closely watching the situation but refused to provide any details about the possible timing of the launch.

"U.S. Army forces in Japan are always vigilant and more than capable of defending Japan from any threat, including ballistic missiles, and as always we are working closely with our Japanese allies," Maj. James Crawford, a spokesman for the U.S. Army in Japan, said Tuesday.

Japan, which is within easy range of the North's arsenal, has long been anxious about missile activity from North Korea, which in 1998 launched a long-range ballistic missile over its main island and well into the Pacific, almost reaching Alaska.

Since then, Japan and the United States have worked together on ballistic missile defense and have built a multibillion dollar ballistic missile shield that includes interceptor missiles both onboard ships at sea and Patriot missile units that ring Tokyo and are also positioned on the island of Okinawa — where more than half of the 50,000 U.S. troops in Japan are deployed.

North Korea unsuccessfully test-fired a long-range missile in 2006 — the same year it conducted its first nuclear test — but is believed to have made improvements in its missile capabilities.

Officials say Misawa is a front-line station for monitoring North Korean activity. If U.S. military satellites detect a flash of heat from a missile range in North Korea, within seconds computers at the base can plot a rough trajectory.

Analysts say North Korea's latest threat is a bid to draw President Barack Obama's attention as his administration formulates its North Korea policy as international disarmament talks remain on hold. Obama's envoy on North Korea is heading to the region for talks with his counterparts to the nuclear talks.

The Associated Press contributed to this report.