WikiLeaks founder Julian Assange pleaded guilty in a US court to receiving and publishing US military secrets after striking a deal with prosecutors that ensured his freedom.

Assange, 52, who is viewed by some as a free-speech activist and by others as a criminal, was flown to this unusual location on a private jet, honoring his wish not to set foot on the continental United States. The case against him was heard in Saipan, the capital of the Northern Mariana Islands, a small American territory in the Pacific Ocean near his native Australia.

During the three-hour hearing, as a result of the deal with US prosecutors, Assange admitted to one felony count of conspiring to obtain and disclose classified documents related to US national defense. He asserted that he believed the First Amendment to the US Constitution, which protects free speech, provided him with protection. "Working as a journalist, I encouraged my source to provide information that was said to be classified in order to publish that information," he told the court. "I believed that the First Amendment protected this activity, but I accept that it was ... a violation of the Espionage Act," Assange said.

The judge sentenced him to five years in prison, equivalent to the time Assange spent detained in Britain while fighting extradition to the United States, where he could face a much harsher sentence under the anti-espionage law.

Assange left the courtroom a free man but is no longer permitted to visit US soil.