London, UK - Julian Assange has been released from prison and left Britain, WikiLeaks said, as he reached a landmark plea deal with US authorities that brought an end to his years-long legal battle.

"Julian Assange is free," WikiLeaks wrote on X of its founder, who had been detained in Britain for five years as he fought extradition to the US, which sought to prosecute him for revealing military secrets.

He has agreed to plead guilty to a single count of conspiracy to obtain and disseminate national defense information, according to a document filed in court in the Northern Mariana Islands in the Pacific.

A charter plane flew Assange from London to Bangkok, where it had been scheduled to stop for refueling.

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From there it is scheduled to fly to Saipan, capital of the US territory, where Assange will appear in court on Wednesday morning.

Assange is expected to be sentenced to five years and two months in prison, with credit for the same amount of time spent behind bars in the UK.

This means he could return to his native Australia, where the government said his case had "dragged on for too long" and there was "nothing to be gained by his continued incarceration."

The 52-year-old was wanted by Washington for publishing hundreds of thousands of secret US documents from 2010 as head of the whistleblowing website WikiLeaks.

US authorities wanted to put Assange on trial for divulging military secrets about the wars in Iraq and Afghanistan.

Assange was indicted by a US federal grand jury in 2019 on 18 counts stemming from WikiLeaks' publication of a trove of national security documents.

Assange's family expressed deep gratitude for his freedom. His mother, Christine Assange, said in a statement carried by Australian media that she was "grateful that my son's ordeal is finally coming to an end."

Wife Stella, meanwhile, thanked campaigners, writing on X that "words cannot express our immense gratitude."

Assange met his wife while he was holed up in Ecuador's London embassy, then married her in a ceremony in prison. They now have two young children.

Announcement of the deal came two weeks before Assange was scheduled to appear in court in Britain to appeal a ruling approving his extradition to the US. He had been detained in the high-security Belmarsh prison in London since April 2019.

Assange was arrested after spending seven years in Ecuador's London embassy to avoid extradition to Sweden, where he faced accusations of sexual assault that were eventually dropped.

The material he released included video showing civilians being killed by fire from a US helicopter gunship in Iraq in 2007. The victims included two Reuters journalists.

The US has accused Assange under the 1917 Espionage Act, which could have brought a sentence of up to 175 years in prison.

The British government approved his extradition in June 2022.

In the latest twist to the saga, two British judges said in May that he could appeal against his extradition to the US.

The appeal was to address whether, as a foreigner on trial in America, he would enjoy the protections of freedom of speech accorded under the First Amendment to the US Constitution.

President Joe Biden had been under growing pressure to drop the long-running case against Assange.

In February, the Australian government made an official request to this effect and Biden said he would consider it, raising hopes among Assange supporters that his ordeal might end.