Julian Assange has renewed his plea to be "set free" after a United Nations panel confirmed its view that the WikiLeaks founder is a victim of arbitrary detention.
The Working Group on Arbitrary Detention rejected a request by the UK Government to review the case.
In February, the panel found that Britain and Sweden had "arbitrarily detained" Mr Assange, who has been living inside the Ecuadorian Embassy in London for over four years.
The panel said he should be freed and entitled to compensation. It said the UK Government had not presented enough new information to merit a new examination.
Mr Assange said: "Now that all appeals are exhausted I expect that the UK and Sweden will comply with their international obligations and set me free. It an obvious and grotesque injustice to detain someone for six years who hasn't even been charged with an offence."
A statement on behalf of WikiLeaks said the original decision now stands and the UK and Sweden are once again required to "immediately put an end to Mr Assange's arbitrary detention and afford him monetary compensation".
It continued: "Earlier this year the United Nations concluded the 16 month long case to which the UK was a party.
"The UK lost, appealed, and today - lost again. The UN instructed the UK and Sweden to take immediate steps to ensure Mr Assange's liberty, protection, and enjoyment of fundamental human rights.
"Now, the United Nations has found that the United Kingdom's request for review of this decision (filed on March 24) was inadmissible. The United Kingdom has now reached the end of the road in its attempt to overturn the ruling.
"As a member of the Security Council and the United Nations Human Council, the United Kingdom must respect its commitment to the United Nations, and release Mr Assange immediately.
"Now, more than ever, moral leadership is required. Maintaining Mr Assange's effective detention will only serve to green light future abuses against defenders of free speech and human rights."
Mr Assange was questioned earlier this month inside the Embassy about a sex allegation in Sweden which he denies.
Swedish officials were present during the interview.
Ecuador is sending a transcript to Sweden in the next few weeks.
Foreign Office Minister for the Americas, Sir Alan Duncan said: "Julian Assange is not, and has never been, arbitrarily detained in the UK and his continued presence in the Ecuadorean Embassy is entirely self-inflicted. We completely reject the opinion of the UN Working Group and are very disappointed that they will not review their deeply flawed and incorrect position.
"A European Arrest Warrant for an allegation of rape remains outstanding and the UK has a legal obligation to extradite him to Sweden.
"He has exhausted the well-recognised protections available to him under the British legal system. He has been avoiding arrest by choosing to remain in the Ecuadorean Embassy for more than four years now and the UK wants to see a conclusion to this case.
"We continue to encourage Ecuador and Sweden to work together to resolve this frustrating situation and we will continue to work to support that happening."
The Working Group on Arbitrary Detention said its opinions are legally-binding to the extent that they are based on binding international human rights law, such as the International Covenant on Civil and Political Rights (ICCPR).
It added that the opinions are also considered as authoritative by prominent international and regional judicial institutions, including the European Court of Human Rights.