Senior judges are seeking assurances from the US government that a man facing extradition accused of child sex crimes will not be placed on a controversial sex offenders treatment programme.
The judges, sitting at the High Court in London, say ordering fugitive Shawn Sullivan, 43, to be detained on the programme in Minnesota could lead to a real risk of "a flagrant denial" of his human rights.
They delayed making a final decision on whether or not to block extradition and gave the US authorities a June 29 deadline to consider offering assurances.
Sullivan, who has joint Irish-US nationality, is wanted to stand trial for allegedly abusing three American girls in the mid-1990s.
He has been described as one of the US's most wanted alleged sex criminals.
He was arrested in London in June 2010 while living with Ministry of Justice policy manager Sarah Smith, 34, in Barnes, south-west London.
They married while he was held at Wandsworth Prison, before he was granted bail.
His lawyers argued at the High Court at a one-day hearing in April that he could face detention for treatment under a civil commitment order - even if he was not convicted - with no hope of release, in breach of Article 5.1 of the European Convention on Human Rights, which protects against loss of liberty without due process.
Today, Lord Justice Moses said there was "a real risk that if extradited the appellant might be subject to an order for civil commitment within Minnesota, and that amounts to a risk that he would suffer a flagrant denial of his rights enshrined in Article 5.1".
The judge said under the programme "there is no requirement that the offences took place recently nor, indeed, that the misconduct resulted in conviction, provided that the misconduct is substantiated by credible evidence".
Mr Justice Eady said the risk of a flagrant denial of human rights was "more than fanciful".
He added: "That assessment of risk is borne out by the absence of any undertaking up to this point."
Sullivan is appealing against a decision of district judge Howard Riddle at Westminster Magistrates' Court in December 2010 that there was no legal reason why extradition should not go ahead.
He is also challenging the Home Secretary's decision in February last year ordering his removal.
Sullivan is accused of raping a 14-year-old girl and sexually molesting two 11-year-olds in Minnesota between 1993 and 1994.
He left the US as prosecutors filed charges against him and was later found to be living in Ireland. He then came to London using an Irish passport with his name spelt in Gaelic as "O'Suilleabhain".
While living in Ireland, he was convicted of sexually assaulting two 12-year-old girls and given a suspended sentence.