WASHINGTON -- The US charge d'affaires in Tokyo was summoned Tuesday by the Japanese authorities to discuss the alleged rape of a 14-year-old girl in Okinawa by a US Marine, a US official said.

Japanese leaders have voiced outrage over the alleged rape in the southern island and warned the case will heighten opposition to US troops inside the country.

State Department spokesman Sean McCormack said mid-level US embassy officials took the initiative to meet Monday with the Japanese to express "deep regret for this incident" and offer to cooperate fully in the case.

Early on Tuesday, the "charge was summoned in and he met with Japan's vice foreign minister," McCormack told reporters.

The US embassy's charge d'affaires is Joseph Donovan.

McCormack said the US ambassador to Tokyo, Thomas Schieffer, returned Tuesday to his post.

Speaking to reporters earlier, the US spokesman said "rape is a horrendous crime and we take these allegations very seriously. We are working very closely with Japanese officials on the matter."

He also said he senior US officials based in Japan "might make a trip down there to Okinawa," but would not say whether the ambassador himself would travel there.

Japanese Prime Minister Yasuo Fukuda said that the rape "can never be forgiven," a day after the arrest of the 38-year-old suspect who has denied the allegations.

Noting there had been similar cases in the past, Fukuda told a parliamentary committee: "But it happened again. I take this very seriously."

Foreign Minister Masahiko Komura, in unusually blunt remarks, said the alleged crime would inevitably affect government plans on US military relocation.

The United States stations more than 40,000 troops in Japan under a treaty to defend its key Asian ally, which has been officially pacifist since World War II.