In 2006, the two countries signed a pact that called for the realignment of American troops in the country and for a marine base on the island to be moved to a less populated area.

But the newly elected Japanese government is re-examining the deal, caught between increasing public opposition to US troops and its crucial military alliance with Washington.

'Cornerstone' alliance

Mizuho Fukushima, a cabinet minister, called for the removal of the US base [Reuters]
Last month Campbell called on Japan to stick to the 2006 deal and relocate the US Futenma air base in Okinawa.

In written testimony before a Senate Foreign Relations Committee subcommittee on January 21, Campbell said the alliance with Japan was a "cornerstone" of the US engagement in Asia.

Campbell also reiterated Washington's desire to see that the US Marine Corps Air Station at Futenma be transferred to another area on the island by 2014.

He said the US is assisting the Japanese government, led by prime minister Yukio Hatoyama, with its review of the Futenma relocation plan.

Decision postponed

However, Hatoyama has repeatedly postponed his decision on the pact, with members of his own government divided on how to proceed.

Last week, he pledged to resolve the issue by May, just before national elections.

But the issue is a difficult one for the prime minister to juggle, with members of his coalition government calling for all US troops to leave Japan.

At a rally against the base, Mizuho Fukushima, a minister in Hatoyama's cabinet, told a crowd protesters that she wants to see the Okinawa base closed and US troops moved out of Japan entirely.

Meanwhile, opposition to the US-Japan pact is growing louder, as thousands marched through central Tokyo on Saturday.

Labor unionists, pacifists, environmentalists and students called for an end to the US troop presence.

They gathered for a rally at a park, under a banner that read "Change! Japan-U.S. Relations".