Twenty-one-year-old Derrick Foster, of Linden Walk, who is American, was told that he will be deported once he completes his 20-month prison term.

He had pleaded guilty to two charges of sexual assault at a previous hearing in Bury St Edmunds and appeared at Ipswich Crown Court on Wednesday to be sentenced.

His victim had been staying with a friend of Foster's because her family were on US military service in the Middle East, Robert Sadd, prosecuting told the court.

While alone with the girl Foster had, on two separate occasions in August last year, and assaulted her.

Mr Sadd said when the girl's mother had spoken to her daughter on the telephone she had realised she was upset and returned to Suffolk where she was able to gain an outline of what had taken place.

The court heard that initially Foster's family had sent him back to the USA after details of the attacks emerged following advice from USAF legal experts at Mildenhall but he returned voluntarily when it was later confirmed that, because he was a civilian, the British authorities had jurisdiction over the case.

Mitigating, Guy Holland said that Foster, who had been living in the UK for three years, had no previous convictions in this country or the USA.

Mr Holland said it had been Foster's father, a senior non-commissioned officer at RAF Mildenhall, who had obtained legal advice on the base that his son could be dealt with by a court in America but had ensured he returned to Suffolk as soon as it became clear that was not the case.

When interviewed Foster had told officers far more about the offences than they already knew and by doing so avoided the need for his victim to be interviewed at length.

Foster had expressed considerable remorse and accepted that the age of the girl and the nature of the sexual contact he had with her were aggravating features in the case, said Mr Holland.

"His family, although shocked and disgusted by his actions, have supported him," said Mr Holland and told the court they were prepared to make every effort to ensure he was able to comply with all aspects of his sentence.

Judge John Devaux considered a pre-sentence report prepared by the probation service and a victim impact statement from the girl and had concluded that only a prison sentence was appropriate because of the seriousness of the offences and the age of Foster's victim.

Judge Devaux said that Foster was likely to serve half his sentence in custody and the remainder on licence. He was ordered to remain on the sex offenders' register for ten years and was banned indefinitely from working with children.

Judge Devaux also made Foster the subject of a sexual offences prevention order which prohibits him from being in any house with a child under16 unless they are a sibling or their parent is present.