The United States has said it is "disappointed" by Theresa May's decision to block the extradition of Gary McKinnon and has insisted the extradition treaty between Britain and the US is "fair and balanced".

McKinnon was accused by US prosecutors of "the biggest military computer hack of all time" but he claims he was simply looking for evidence of UFOs.

On Tuesday the home secretary intervened to stop extradition of the the 46-year-old, who has Asperger's, humanitarian grounds.

A spokeswoman for the US Department of Justice told The Huffington Post UK that the Obama administration disagreed with the decision but viewed it as an "exceptional" case.

"The United States is disappointed by the UK Home Secretary’s decision not to extradite Gary McKinnon, particularly given the past decisions of the UK courts and prior Home Secretaries that he should face trial in the United States," she said.

"We note that the Home Secretary has described this case as exceptional and, thus, this decision does not set a precedent for future cases.

"The Home Secretary has acknowledged that Mr. McKinnon is accused of serious crimes and that the United Kingdom’s Director of Public Prosecutions will now consider whether Mr. McKinnon has a case to answer in a UK court."

McKinnon's case has led many in Britain to question the fairness of the extradition treaty with the United States. Critics argue it is easier for the American government to extradite British citizens than it is for the UK to extradite American citizens.

A review conducted by Sir Scott Baker for the Home Office decided the Extradition Act was not biased against British citizens.

However a separate review conducted for Nick Clegg by former Lib Dem leader Sir Ming Campbell concluded it was unfair.

"The proper course should be to raise the British standard to the American one, so that UK citizens do not suffer a disadvantage compared to their US equivalents," Sir Ming said.

On Tuesday May announced that she would introduce a "forum bar", as called for by Sir Ming, in extradition cases which would mean a court hearing has to be held to decide whether a person should stand trial in the UK or abroad.

SEE ALSO: What Is A 'Forum Bar' In Extradition Cases?

However she told MPs that Sir Scott's overall view that the treaty was fair was "broadly sound", a statement welcomed by the United States.

"Our extradition relationship with the United Kingdom remains strong, as is demonstrated by the extradition of five alleged terrorists from the United Kingdom just last week," the administration spokeswoman told HuffPost UK.

"At the same time, we are pleased that the home secretary has accepted the finding of Sir Scott Baker’s independent panel that the U.S.-UK extradition treaty brings benefit to both countries.

"The United States fully agrees with the report’s conclusion that the treaty is fair and balanced.

She added: "The law enforcement relationship between the United States and the United Kingdom has always been predicated on trust, respect, and the common goals of protecting our nations and eliminating safe havens for criminals.

"Our extradition treaty serves the interests of both our nations, and the United States values our continuing collaboration with British law enforcement authorities on a myriad of shared concerns."

May has been widely praised for blocking McKinnon's extradition, which many saw as a case of the British David standing up to the American Goliath.

However former Labour home secretary Alan Johnson questioned whether the move would damage UK-US relations, suggesting it was merely done to increase the popularity of the government.

Johnson told MPs he thought May had made the decision "in her party's best interest; it is not in the best interests of the country".

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  • Janis Sharp, mother of Gary McKinnon, at

    Janis Sharp, mother of Gary McKinnon, attends a protest outside the Home Office against the Home Secretary's decision not to halt his extradition to the US, in Central London on December 15, 2009. Gary McKinnon, who suffers from a form of autism, could spend life in prison if convicted by a US court of gaining access to 97 computers in 2001 and 2002 in the aftermath of the September 11, 2001 attacks. AFP PHOTO/Ben Stansall

  • Janis Sharp (2nd R), mother of Gary McKi

    Janis Sharp (2nd R), mother of Gary McKinnon, Liberal Democrat Leader Nick Clegg (3rd R) and Liberal Democrat Chris Huhne (4th R) attend a protest outside the Home Office against the Home Secretary's decision not to halt his extradition to the US, in central London, on December 15, 2009. Gary McKinnon, who suffers from a form of autism, could spend life in prison if convicted by a US court of gaining access to 97 computers in 2001 and 2002 in the aftermath of the September 11, 2001 attacks. AFP PHOTO/Ben Stansall

  • Gary McKinnon extradition

    Computer hacker Gary McKinnon's mum Janis Sharp with a letter and flowers she is planning to give to the Queen.

  • Gary McKinnon extradition

    Computer hacker Gary McKinnon's mum Janis Sharp with his girlfriend Lucy Clark with a letter and flowers they plan to give to the Queen.

  • Gary McKinnon extradition

    Janis Sharp, holds a card signed by politicians and well wishers for her son, computer hacker Gary McKinnon, on Westminster Bridge, London, as authorities in the US want him to stand trial for hacking into top secret military computers, Mr McKinnon, from Wood Green, north London, suffers from Asperger's syndrome, says he was looking for evidence of UFOs.

  • Gary McKinnon extradition

    Janis Sharp (right) the mother of Gary McKinnon with Trudie Styler, as outside number 10, Downing Street, handing in a book and poems written by Gary, to mark the 10 years since her son's arrest on US hacking allegations.

  • Gary McKinnon extradition

    Janis Sharp (right) the mother of Gary McKinnon with Trudie Styler, as they stand outside number 10, Downing Street, before handing in a book and poems written by Gary, to mark the 10 years since her son's arrest on US hacking allegations.

  • Decision Expected On The Extradition Of Computer Hacker Gary McKinnon

    LONDON, ENGLAND - OCTOBER 16: Janis Sharp, the mother of British computer hacker Gary McKinnon, is photographed as she attends a press conference following a decision by Home Secretary Theresa May not to extradite Mr McKinnon to the US on October 16, 2012 in London, England. Mr McKinnon, who sufferers from Asperger''s Syndrome, admits to accessing US Government computers but claims he was looking for evidence of UFOs. Mrs May told MPs in the House of Commons that Mr McKinnon was 'seriously ill' and that enforcing the extradition warrant would be in breech of his human rights. (Photo by Oli Scarff/Getty Images)

  • Janis Sharp, the mother of computer hacker Gary McKinnon leaves her home near Hatfield, England, Tuesday, Oct. 16, 2012. Britain's government says Gary McKinnon won't be extradited to the United States, ending his decade-long campaign to avoid trial there over allegations he broke into sensitive military and NASA computer networks. (AP Photo/Kirsty Wigglesworth)

  • Janis Sharp, the mother of British computer hacker Gary McKinnon reacts, during a news conference in London, Tuesday, Oct. 16, 2012. A British computer hacker's decade-long struggle to avoid trial in the U.S. over alleged breaches of military and NASA networks ended in success Tuesday, as the U.K. government ruled he was unfit to face charges there. Home Secretary Theresa May said she had blocked the U.S. request to extradite Gary McKinnon after medical experts concluded he was seriously depressed and that there was "a high risk of him ending his life." (AP Photo/Matt Dunham)

  • Decision Expected On The Extradition Of Computer Hacker Gary McKinnon

    LONDON, ENGLAND - OCTOBER 16: Janis Sharp, the mother of British computer hacker Gary McKinnon, is interviewed after a press conference following a decision by Home Secretary Theresa May not to extradite Mr McKinnon to the US on October 16, 2012 in London, England. Mr McKinnon, who sufferers from Asperger''s Syndrome, admits to accessing US Government computers but claims he was looking for evidence of UFOs. Mrs May told MPs in the House of Commons that Mr McKinnon was 'seriously ill' and that enforcing the extradition warrant would be in breech of his human rights. (Photo by Oli Scarff/Getty Images)

  • Janis Sharp, the mother of British computer hacker Gary McKinnon reacts, during a news conference in London, Tuesday, Oct. 16, 2012. A British computer hacker's decade-long struggle to avoid trial in the U.S. over alleged breaches of military and NASA networks ended in success Tuesday, as the U.K. government ruled he was unfit to face charges there. Home Secretary Theresa May said she had blocked the U.S. request to extradite Gary McKinnon after medical experts concluded he was seriously depressed and that there was "a high risk of him ending his life." (AP Photo/Matt Dunham)

  • McKinnon extradition

    Janis Sharp, mother of Gary McKinnon, arrives for a press conference at her solicitors in London today.

  • McKinnon extradition

    Janis Sharp, mother of Gary McKinnon, arrives for a press conference at her solicitors in London today.

  • McKinnon extradition

    A supporter of Gary McKinnon congratulates his mother, Janis Sharp, before a press conference at her solicitor's in London today.

  • McKinnon extradition

    Janis Sharp, mother of Gary McKinnon arrives for a press conference at her solicitors in London today.