Julian Assange's lawyer says he will not be leaving Ecuador's embassy in London until it is guaranteed he will not be extradited to the United States.

The Australian founder of WikiLeaks overnight declared that he would leave the embassy, where he has been holed up for two years, "soon".

The 43-year-old, who is reportedly suffering from heart and lung problems, made the comments during a press conference amid speculation he was set to hand himself over.

Swedish prosecutors want to question Mr Assange over sexual assault allegations made by two female former WikiLeaks volunteers.

Mr Assange denies the allegations and has been fighting a legal battle against extradition since his arrest in Britain in 2010.

He says he fears he will be arrested and extradited to the US if he steps outside the embassy.

This morning lawyer Jennifer Robinson told ABC News Breakfast the two-year stay in the embassy had had a "significant" impact on Mr Assange's health.

"[He will leave] as soon as conditions can be negotiated that allow Julian to leave the embassy while his political asylum, to protect him from the risk of extradition to the US, [is] respected. And we haven't seen that happen yet," she said.

"We'd all like to see him out of there as soon as possible. He's been in there more than two years and the circumstances and the conditions inside the embassy aren't great.

"He hasn't been outside for two years. There's nowhere for him to exercise and that's having significant impacts on his health.

"But it remains to be seen when we'll be able to negotiate and when Ecuador will be able to negotiate conditions which would make it possible for him to leave.

"We have been asking that there be assurances given that he will not be extradited to the US, that is and has always been his main concern, and indeed is the reason for the grant of asylum that's seen him remain inside the embassy.

"It's very difficult to put a timeline to this," she continued.

"As Julian said, he'd like to be leaving the embassy soon, we'd all like to see that happen, but there are a complicated number of legal cases that are ongoing both in Sweden, and the ongoing grand jury investigation in the US which is reason for his asylum.

"We hope those assurances will be given. We'd like to see the grand jury close so he can go back to Sweden and clear his name. That would be the preferable outcome for everyone."

Ms Robertson said Mr Assange had been refused permission to travel to hospital to seek treatment for his medical conditions.

"If he is required to leave the embassy for hospital treatment he would be arrested," she said.

"This is a very serious situation and is the reason that this case has been taken up at the UN by more than 60 human rights groups around the world because of the impact on Julian's health and human rights."

Swedish prosecutor criticised

Ms Robinson says she does not understand why a Swedish prosecutor is refusing to come to London to interview Mr Assange so the case can proceed.

"We've asked for her to come to London to interview him so the matter can be progressed and he can clear his name and she has refused," she said.

"Julian's remarks also last night refer to the fact that there's an ongoing appeal in Sweden that will be heard at the end of the European summer in which we're challenging his arrest warrant.

Sorry, this video has expired Assange leaving Ecuadorian embassy 'soon'

"Should that be successful we're hoping they will be progressing his case and he will actually be able to leave the embassy."

Ms Robinson says the Swedish prosecutor is not acting in accordance with European law on human rights.

"It is a principle of European law that if you're going to invade on someone's human rights that you take the means that are least intrusive into breaching the human rights, and the prosecutor has not done that," she said.

"She has the ability under Swedish law and under mutual legal assistance to interview him in London, and indeed the Swedish supreme court judge, when he was the president of the Supreme Court of Sweden when he was here in Australia, said they could not offer a reason why she has not done that.

"It's been four years and she has an obligation under European law to take the most proportionate step - and she hasn't done so."

Ms Robinson says the case has set a precedent that has been of great concern in the UK.

"Julian's case, of course, meant that anyone can be extradited from anywhere - anyone from the UK can be extradited to anywhere in Europe without being charged, without being shown the evidence, and in circumstances where that hasn't been approved by a judge," she said.