Top Japanese officials on Tuesday denounced the suspected rape of a 14-year-old girl by a U.S. Marine on the southern island of Okinawa, an episode with echoes of a 1995 case that jolted the U.S.-Japan alliance.

The Marine, 38-year-old Tyrone Hadnott, based at Camp Courtney on the island, was arrested on Monday on suspicion of raping the schoolgirl when the two were in a car on Sunday.

He has denied raping the girl but acknowledged forcing her to kiss him, Japanese media said.

"It is unforgivable," Prime Minister Yasuo Fukuda told a parliamentary panel in his first public comments on the latest incident on Okinawa, host to a huge U.S. military presence.

"It has happened over and over again in the past and I take it as a grave case."

Defence Minister Shigeru Ishiba expressed anger over repeated incidents despite frequent promises by U.S. officials to prevent them. "This will have a big impact on future U.S-Japan relations," he told a news conference.

In 1995, the rape of a 12-year-old Japanese schoolgirl by three U.S. servicemen sparked huge protests calling on the U.S. military to leave Okinawa, where residents have long resented crime, noise and accidents they blame on the U.S. presence.

But diplomatic experts said such political fallout could be limited this time if the two governments were careful.

"I don't see that there is the sort of dry kindling there for this to light," said Derek Mitchell, a senior fellow at Washington-based Centre for Strategic and International Studies.

"I think the alliance is on much more solid ground."

The 1995 rape case coincided with bitter trade talks on Japan's auto market as well as doubts about the significance of the alliance after the end of the Cold War.

Japan is home to some 50,000 U.S. troops, under a security alliance that is a pillar of Japan's postwar diplomacy.

OKINAWA REACTION KEY

Both U.S. and Japanese authorities want to prevent a re-run of 1995 but analysts said much depends on the reaction in Okinawa.

Okinawan officials have expressed outrage and on Tuesday they lodged formal protests with the Marines, while the central government decided to send a senior diplomat to the island.

"U.S.-Japan relations are not just a matter of the bases," said main opposition Democratic Party leader Ichiro Ozawa.

"But (incidents concerning) military bases and Okinawa ... are likely to have a big emotional impact on the people."

However, unlike in 1995 when the Okinawa governor was a staunch critic of the bases, the current governor was elected with ruling party backing and is inclined to support Tokyo on U.S. military issues.

U.S. officials have responded quickly to mitigate fallout from the case, which comes as Tokyo tries to persuade Okinawa residents to accept a plan to relocate the Marine's Futenma Air Station from the densely populated central Okinawa city of Ginowan to the coastal city of Nago.

"Obviously, the U.S. military is cooperating with the Okinawan authorities who are investigating this," Pentagon spokesman Bryan Whitman said in Washington, adding, however, that the Marine was presumed innocent until proven guilty.

"I wouldn't tie our long-term strategic relationship with Okinawa, that part of the world to this particular incident."

The Futenma move is part of a broader plan to move some 8,000 Marines from Okinawa to Guam.