LONDON (Reuters) - Prosecutors on Monday questioned WikiLeaks founder Julian Assange at the Ecuadorian embassy in London, where he has been holed up for four years, in an investigation into allegations that he committed rape in Sweden in 2010.

Assange, who enraged Washington by publishing a flood of secret U.S. diplomatic cables, fled to the embassy for fear that, if extradited to Sweden, he could be sent on to the United States and face a long prison term there for leaking U.S. secrets.

Swedish Chief Prosecutor Ingrid Isgren spent around four hours in the embassy, where she posed questions through an Ecuadorian prosecutor, before leaving without making comment.

Ecuador, which helped Assange avoid extradition by granting him asylum after he fled to its London legation, agreed to help Swedish prosecutors question Assange, who has denied the rape allegation.

“Today, after six years of offering his statement to the Swedish authorities, Julian Assange has finally been afforded the opportunity to do so,” WikiLeaks said in a statement.

But it complained that Assange’s Swedish lawyer, Per Samuelson, was not notified or summoned to attend the session, and his absence was “a clear breach of process”.

A member of Assange’s legal team, Melinda Taylor, said procrastination on the part of Swedish investigators had denied Assange any right to clear his name.

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“As a result of six years of delays and over four and a half years of illegal and arbitrary detention, Mr Assange is today faced with (a) Hobson’s choice: either he gives a statement in which his health, memory and psychological state are severely impeded, or, he is denied once more, an opportunity to be heard,” she said by email.

The 45-year-old Australian has refused to go to Sweden for questioning, saying that would expose him to further extradition to the United States, where a criminal investigation into the publication of secret documents by WikiLeaks continues.

In 2010, WikiLeaks published thousands of classified U.S. military and diplomatic documents in what became one of the largest information leaks in U.S. history.

Assange made international headlines in early 2010 when WikiLeaks released classified U.S. military video showing a 2007 attack by Apache helicopters that killed a dozen people in Baghdad, including two Reuters news staff.

EMBASSY QUESTIONING

Under conditions agreed by Ecuador, Isgren and a police investigator asked questions through the Ecuadorian prosecutor, who will then report the findings to Sweden, which will then decide whether to continue the investigation.

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Samuelson, Assange’s Swedish lawyer, said he had been barred from the meeting. “Ecuador refuses to let me in and insists that the questioning will continue without my presence, against my client’s wishes to have me there,” he told Reuters.

While Assange’s Ecuadorean defense lawyer appeared to be present, Samuelson said he still hoped to be admitted if the interview continued. “But a good chunk of questioning has already taken place as far as I understand,” he said.

A Swedish appeals court decided in September to uphold Assange’s arrest warrant, saying a strong public interest argument outweighed a case to set it aside based on the lengthy deadlock and a previous lack of impetus in pursuing the case.

Assange’s request to have the warrant overturned came after a U.N. panel assessed in February that his stay at the Ecuadorean embassy amounted to arbitrary detention, and said he should be let go and be awarded compensation.

Even if Sweden drops the investigation, however, Assange could be arrested for breaching bail conditions in Britain.