A South Korean court has sentenced an American soldier to 10 years in prison for raping a teenage girl, the heaviest sentence handed a U.S. serviceman in the country in almost 20 years.

The court said Tuesday the unidentified soldier had committed sadistic and sexually perverted acts in which he repeatedly raped the 18-year-old girl over a period of three hours while threatening her with a pair of scissors.

Senior U.S. diplomats have offered apologies for the rape, which took place in September in a boarding room near Seoul. It was the harshest sentence handed to any U.S. service member in South Korea since 1993 when a soldier received a life sentence for murdering a South Korean woman.

The United States maintains about 28,500 troops in South Korea, where they are tasked with helping to defend the country against any threat from North Korea.

Criminal actions by the soldiers are a major source of friction between the countries. Large-scale protests broke out in 2002 after a U.S. armored vehicle killed two schoolgirls in a traffic accident.

Prosecutors had asked for a longer sentence in Tuesday's case, but the court said it took into account the fact that the 21-year-old private has repented and had no prior criminal record.