LONDON — Britain’s High Court blocked a US government bid Thursday to extradite a sex criminal to Minnesota, saying the state’s restrictive treatment program for sex offenders was far too draconian.

Judges Alan Moses and David Eady endorsed 43-year-old Shawn Sullivan’s appeal against extradition after US authorities refused to guarantee that Sullivan wouldn’t be placed in Minnesota’s civil commitment program, which provides for the indefinite detention of people found to be ‘‘sexually dangerous.’’

The judges said that commitment to the program would be in ‘‘flagrant denial’’ of Sullivan’s human rights.

Sullivan, a dual US-Irish citizen, is accused of raping a 14-year-old girl and sexually molesting two 11-year-olds in Minnesota in the 1990s. He escaped to Ireland as prosecutors prepared to file charges, and while staying there was convicted of sexually assaulting two 12-year-old girls.

Authorities finally caught up with him two years ago in London.