Wikileaks founder Julian Assange has lost his UK Supreme Court fight against extradition to Sweden to face accusations of sex offences.
Lord Phillips, the court's president, said a majority of five justices to two had ruled against Mr Assange.
The court ruled the extradition request had been "lawfully made".
However, Mr Assange has 14 days to challenge the ruling and his solicitor, Gareth Peirce, said his lawyers would be asking the court to reconsider.
Mr Assange, who has been on conditional bail in the UK, did not attend the hearing in central London. His lawyer later told reporters he had been "stuck in traffic".
Following the hearing, he tweeted: "We got the news not hoped for."
The Wikileaks website published material from leaked diplomatic cables, embarrassing several governments.
The 40-year-old Australian is accused of raping one woman and "sexually molesting and coercing" another in Stockholm in August 2010, but he claims the allegations against him are politically motivated.
His lawyers had asked the court to block his extradition, arguing that a European arrest warrant issued against him was "invalid and unenforceable".
The key legal question was whether the Swedish prosecutor who issued it had the "judicial authority" to do so under the 2003 Extradition Act - or whether the words gave that power only to a court or a judge.
Lord Phillips said five of the seven Supreme Court justices had agreed the warrant was lawful because the prosecutor could be considered a proper "judicial authority" even if this was not specifically mentioned in legislation or international agreements.
However, this point of law had not been simple to resolve, said Lord Phillips, and two of the justices, Lady Hale and Lord Mance, had disagreed with the decision.
Lord Phillips said the meaning of the words had been debated in Parliament when the Extradition Act was being drawn up and at least one minister had - in his view, wrongly - said they could only apply to a court or judge.
But Dinah Rose QC, for Mr Assange, said she could challenge the Supreme Court's decision because it relied on a 1969 convention relating to how treaties - such as those concerning extradition - should be implemented, and this had not been discussed during the hearing.
In a statement, the Supreme Court said: "Ms Rose suggested that the majority of the court appear to have based their decision on the interpretation of the Vienna Convention on the Law of Treaties, on which no argument was heard and no opportunity of making submission was given.
"The Supreme Court has granted Ms Rose 14 days to make such an application.
"If she decides to do so, the justices will then decide whether to re-open the appeal and accept further submissions either verbally through a further hearing, or on paper, on the matter."
The decision to stay the extradition order means that it cannot become active until at least 13 June.