Ecuador has accused Sweden of a "lack of initiative" in completing an ongoing investigation into WikiLeaks founder Julian Assange.

In a letter to the Swedish government, Ecuadorean authorities expressed concern about the "serious lack of progress" in dealing with his case, the BBC reported. They claim that there has been a "serious failure" by Sweden's prosecutor to bring the inquiry into sexual assault allegations, which date back to 2010, to a close.

Assange has been living at the Ecuadorean embassy in London for almost five years. The British government has said that Assange will be arrested if he leaves the embassy, where he has been granted asylum and is beyond the reach of UK authorities.

He fears that he will be extradited to the US and charged with espionage if he leaves. The Australian computer programmer released more than 500,000 confidential US military files on the wars in Afghanistan and Iraq in 2010.

At the time of the leaks, a request was made for Assange's extradition to Sweden, where he had been questioned months earlier over allegations of sexual assault and rape. In 2010, a woman accused the WikiLeaks founder of raping her in Stockholm while he was visiting the city to give a lecture. Assange has denied the accusation, claiming that it is politically motivated.

Sweden's chief prosecutor, Ingrid Isgren, visited Assange for the first time at the Ecuadorean embassy in December 2016. No details of the visit were made known.

The letter also revealed the views of several members of President Trump's administration on the case, including CIA boss Mike Pompeo who described WikiLeaks as a "hostile intelligence service" that made it more difficult for the US intelligence service to protect Americans.

In April, US Attorney General said arresting Assange was a "top priority" but so far no charges have been brought.