Ecuadorean diplomats seek UK assurances that WikiLeaks founder will not be extradited to US after proceedings in Sweden

The Ecuadorean government is seeking to avert the "evil" of the extradition of Julian Assange to the US, according to a senior legal adviser to the country's embassy in London, where the WikiLeaks founder has sought sanctuary with a view to claiming asylum.

Diplomats for the small Latin American country said they had been seeking assurances from the UK that Assange would not be extradited to the US after the completion of legal proceedings in Sweden, where he is wanted for questioning over allegations of sexual assault.

Lawyers for Assange, who has been living in the Ecuadorean embassy for five weeks, believe there are secret plans to extradite him to the US to face trial, possibly for conspiracy to commit espionage. If found guilty, the 40-year-old could face life imprisonment.

Two officials at the Ecuadorean embassy said it had been seeking assurances from both the UK and Sweden that Assange would not be eventually sent to the US, but had received no answer. They said Ecuador would now formally ask the US if there were any legal proceedings against Assange or "an investigation which has identified him as a target and which may result in a later extradition request".

The senior legal adviser said: "In legal terms … the evil that Ecuador wishes to prevent is the extradition [of Assange] to the US. Now if there are ways and means of that being tied down, I think that would be a just solution."

Assange first sought refuge in the Ecuadorean embassy, citing the UN declaration on human rights, on 19 June. Ever since, he has been living in the ground-floor embassy in a small, square room, which friends who have recently visited estimate is around 15ft wide.

The embassy, near the Harrods department store in Knightsbridge, has no courtyard, so Assange has been given exercise equipment. But he remains confined to the small room and adjoining corridor, with a window that barely opens.

Meanwhile, diplomats at the embassy have spent recent weeks seeking to negotiate a solution to the legal impasse. Assange remains on bail after losing his last supreme court appeal against extradition to Sweden, where he is wanted for questioning in connection with accusations of sexual assault and rape in Stockholm in 2010.

If he leaves the premises, he is liable to immediate arrest by the Metropolitan police, which has stationed two officers outside the building.

A political adviser to the Ecuadorean government said Assange's asylum claim had presented the country with "an absolutely extraordinary case" that placed it at the centre of a global controversy involving four other countries: the UK, Sweden, the US and Australia, where Assange was born and remains a citizen.

Ecuador was seeking to be an "honest broker", he said, while meeting its international obligations. He said that on Wednesday, Ecuador formally offered the Swedish prosecutor the opportunity to interview Assange inside the London embassy. Sweden had not responded to the proposal.

Most of the discussions have focused on seeking to establish whether, once Swedish legal proceedings against Assange are resolved, there will be any attempts to extradite him to the US.

He said Ecuador was "deeply concerned" at the prospect of Assange's extradition to a country which has the death penalty. "Ecuador has also raised the point – and is very much concerned about – life sentence," he said. "According to our law, life sentence may be equally inhumane, in the sense that any person that has no prospect of leaving confinement is, in fact, as we see it, condemned to a death sentence [for] life. For us, that is equally inhumane."

Assange's US lawyer, Michael Ratner, said he was certain Assange had already either been secretly indicted by a grand jury in Washington or would face extradition with a view to prosecution. He believed the death penalty remained a possibility.

"I have no doubt there is a serious investigation, which has gone on, and is continuing, into Julian Assange and WikiLeaks," he said. However, Ratner said it was highly unlikely the US would confirm to Ecuador or any other party that it intended to prosecute Assange.

Ever since Assange unexpectedly sought refuge at the embassy five weeks ago, diplomats have been in regular discussions with both the Swedish and UK governments.

The two officials estimated there had been more than 20 meetings – including video conferences – with the UK Foreign Office. There had also been around 10 meetings arranged between Ecuadorean and Swedish diplomats, they said.

Diplomatic discussions were said to have been "friendly and polite".

The Ecuadoreans said discussions had focused on what was likely to happen to Assange once legal proceedings in Sweden were completed.

The senior legal adviser said that under extradition law, the concept of "specialty" ensures an individual can only be extradited to one country – in the case of Assange, Sweden. Once legal proceedings in that country have been completed, the individual is given a 45-day leave, during which they are free to go where they want.

Assange should, therefore, be free to travel to any other state – including the UK, Ecuador or Australia – once legal proceedings against him are completed in Sweden.

However, specialty can be waived by the country granting the initial extradition request – in this case the UK – thereby allowing an individual to be extradited to a third country.

The senior legal adviser to the Ecuadoreans said that the home secretary, Theresa May, would need to waive specialty under section 58 of the Extradition Act 2003, before Assange could be extradited from Sweden to the US.

Despite repeated requests from Ecuador, the Foreign Office has not said whether or not May intends to exercise her powers to allow for any potential future extradition to the US.

"The concerns that Ecuador has in relation to that whole process is that some states – not least of which the US – have been known to hold back on their extradition requests, to a timely moment, when they can serve the process with greatest impact," the senior legal adviser said. "And so the concern would be that the US has in mind a request for extradition on the basis of WikiLeaks charges."

The officials said they did not expect a decision to be made on Assange's asylum claim until after the Olympics.

A spokesman for the Foreign Office said: "Since Mr Assange first entered the Ecuadorean embassy five weeks ago, we have repeatedly made clear to the Ecuadorean government that the UK has a binding legal obligation to extradite Mr Assange to Sweden to face questioning over allegations of sexual offences. We have been seeking a diplomatic solution and expect Ecuador to resolve this issue in accordance with its international obligations.

"The UK courts, including the supreme court, have confirmed that Mr Assange's extradition to Sweden complies with all the requirements of the UK's Extradition Act, including as regards the protection of his human rights. We have gone to great lengths to explain to Ecuador the human rights protections inherent in our law."