TOKYO - JAPAN vowed to crackdown on crimes involving American troops based in the country after a surprise decision by prosecutors not to pursue rape charges against a United States Marine, reports said.

Staff Sergeant Tyrone Luther Hadnott, who had been accused of raping a 14-year-old, was freed from custody late on Friday after the girl's family decided not to pursue the case.

The initial case against Hadnott - who was released 18 days after his arrest on the southern island of Okinawa - triggered outrage in Japan and reignited controversy surrounding the presence of thousands of US troops.

Hadnott, 38, was immediately taken into custody by the US military, which said it would conduct its own inquiry.

Prosecutors said the girl's family had decided not to pursue the allegations against Hadnott as the girl did not want to be part of a high-profile case.

Mr Yaichiro Yamashiki, chief public prosecutor in Naha, Okinawa's prefectural capital, was quoted by local media as saying the girl had told investigators: 'I don't want to be involved in (the case) any more. Please leave me alone.'

Japan's Foreign Minister Masahiko Komura confirmed the charges against Hadnott would not be pursued.

'Japan will not exercise jurisdiction' in the case, the Maninichi Shimbun on Saturday quoted him telling reporters.

'But can such a case happen again? It's a different story,' he said.

'We will continue making an effort to take preventive measures together with the US military,' he said.

Prime Minister Yasuo Fukuda told reporters late on Friday the two countries should cooperate to prevent similar incidents in future.

'Japan and the United States should work hard together to prevent such a case from happening again,' he told reporters. 'I want to continue to do my best on the issue.'

Police had said Hadnott admitted trying to forcibly kiss the teenager but denied rape and said he did not know that she was underage.

Okinawa City Mayor Mitsuko Tomon was quoted saying of the girl: 'I presume she had a hard time as the case had a great impact.

'But the crime itself has not disappeared. I would like to continue lodging a strong protest to the country and the military, urging them to ensure such cases never happen again,' he said, referring to the United States.

Okinawa residents and protesters said they would press ahead with planned rallies in Okinawa, despite the charges against Hadnott having been dropped.

The outrage over the rape allegations led the US military to enforce a sweeping curfew on all troops and their families in Okinawa, base for half of the more than 40,000 US troops stationed in Japan.

US authorities had moved quickly to try to contain damage from the case, with Secretary of State Condoleezza Rice offering an apology on behalf of Washington during her trip to Tokyo earlier in the week.

The case was the most high profile of a series of incidents on Okinawa.

Authorities are also investigating separate allegations that a US serviceman raped a Filipina in a hotel on Feb 18.

In 1995, three US troops gang-raped a 12-year-old girl, setting off major protests that set in motion a process to withdraw thousands of troops from Okinawa.

Under Japanese law, prosecutors cannot press charges in a rape case unless the victim agrees to pursue the allegations.