Admiral Gary Roughead, commander of the US Pacific Fleet, said the navy planned to base the USS Shiloh at Yokosuka, a major port southwest of Tokyo, later this year.

The USS Shiloh "will have the most advanced ballistic missile defense capability on board," he said in Washington on Tuesday.

Japan is developing a missile defense system with the United States in the face of threats from North Korea, but currently it does not have the ability to intercept them.

Japan was barred from possessing an armed forces under the US-imposed post-World War II constitution, which the government is seeking to revise.

Japanese opposed to upgrading military ties with the United States reacted skeptically to the planned relocation of the USS Shiloh.

"It would lead to a strengthening of the Yokosuka base," said Masahiko Goto, an attorney who is campaigning against a US-Japan agreement last year to station a nuclear-powered US aircraft carrier at Yokosuka from 2008.

"Missile defense is essentially to protect mainland America" rather than Japan, he argued.

"They want to detect a missile fired from North Korea or China towards America while it is over the Sea of Japan and before it reaches their mainland," Goto said.

South Korea says Pyongyang is developing a long-range missile with a range of 6,700 kilometers (4,150 miles) that would put the United States' western seaboard within reach.

Pyongyang shocked Asia in 1998 by test-launching over Japan a Taepodong-1 missile, which has a range of up to 2,000 kilometers (1,250 miles).

The Shiloh plan comes as Japanese activists try to block a realignment deal reached last year between the United States and Japan.

Some 7,000 of the 40,000 US troops in Japan would leave under the agreement, but local campaigners are pushing for a greater pullout.

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