Britain has warned it will not allow Julian Assange safe passage out of the country after the WikiLeaks founder was granted political asylum by Ecuador.

The South American country, which has been harbouring Assange in London, last night declared his own government in Australia had failed to protect his rights.

Ecuador’s decision dramatically heightens its diplomatic standoff with Britain, where the 41-year-old Australian citizen is holed up in the Ecuadorian embassy surrounded by British police keen to arrest him for skipping bail.

British Foreign Secretary William Hague said he was “disappointed” and that diplomatic immunity should not be used to harbour alleged criminals.

“We will not allow Mr Assange safe passage out of the United Kingdom, nor is there any legal basis for us to do so,” Mr Hague said.

“Under our law… British authorities are under a binding obligation to extradite him to Sweden,” he added, committing to uphold the ruling of British courts, which have deemed Assange should face questioning in Stockholm for allegations of sexual assault.

Ecuador demanded the United Nations organise safe passage for Assange to South America after it granted him asylum.

“Ecuador has determined that Mr Assange does not have the due protection and support that he should be receiving from the state of which he is a citizen,” Foreign Minister Ricardo Patino told a press conference last night.

Assange said the decision was “a significant victory for myself, and my people”.

“Things will probably get more stressful now,” he said.

WikiLeaks announced that Assange would make a statement on Sunday in front of the Ecuadorian embassy.

“Sunday the 19th is two months exactly since Assange entered the embassy. It will be his first public appearance since March,” the organisation said.

Scuffles broke out last night between police and Assange supporters outside the embassy, with at least three protesters arrested.

Apart from accusing Australia of neglecting its duties to Assange, Ecuador also slammed Sweden, which is seeking to extradite him on allegations of sexual assault, and the US.

Mr Patino said Swedish authorities “have not allowed him legitimate rights to a fair defence” on sexual assault allegations and insisted the US could be seeking to subject him to the death penalty and “would not provide him with a fair trial”.

Sweden today rejected the claim that Assange would not get a fair trial as a reason for granting him political asylum, and summoned the South American country’s envoy to explain.

“Our firm legal and constitutional system guarantees the rights of each and everyone. We firmly reject any accusations to the contrary,” Foreign Minister Carl Bildt said on his Twitter account.

Separately, Swedish foreign ministry spokesman Anders Joerle said: “The Ecuadorian ambassador is expected at the ministry as soon as possible.

“The accusations that (the Ecuadorian foreign ministry) has formulated are serious and it is unacceptable that Ecuador would want to halt the Swedish judicial process and European judicial co-operation.”

Washington denied it was lobbying Britain to take Assange into custody.

“With regard to the charge that the US was intent on persecuting him, I reject that completely,” State Department spokeswoman Victoria Nuland said.

“It is an issue among the countries involved and we are not planning to interject ourselves.”

Ecuador’s record on human rights and freedom of speech have been regularly criticised by international human rights groups, but its government said it was seeking to defend Assange to protect the freedom of speech and the work of the whistleblowing website.

Ecuador sought to escalate and broaden the diplomatic confrontation by saying it had asked regional South American governments to support it against an extraordinary threat by the British government that British police could potentially invade the embassy to arrest Assange.

Mr Patino said that Ecuador had already received expressions of solidarity “from political leaders in several countries”.

Eight weeks after Assange fled to the Ecuadorian embassy to avoid extradition to Sweden, Mr Patino said the Australian had requested asylum because of “his fear that he would be handed over either by the British, Swedish or Australian authorities to the US”.

Assange had successfully convinced the Ecuadorian government that he was “a victim of prosecution in different countries which is a result not only of his ideas but also his work in publishing the truth about mass corruption and abuses of human rights all over the world”, Mr Patino said.

“The legal evidence shows that if there is an extradition to the USA he would not have a fair trial and he would be judged in special or military tribunals and it is not impossible that he would be treated in a cruel manner or even given the death penalty.”

In Canberra, federal Attorney-General Nicola Roxon said Australia would not intervene in the extradition debate.

Opposition Leader Tony Abbott said this morning that Assange should be subject to British law like any other citizen.

“Whatever the ordinary law of Britain is, whatever would happen to anyone else in the same circumstances, Julian Assange should get identical treatment to anyone else in a similar position,” he told the Nine Network.

Assange’s mother thanked the government of Ecuador but said she did not know what her son’s next move would be.

Christine Assange said in Brisbane: “I don’t think anybody in the international sphere can say that this was not a well-considered decision.”

“I’m just extremely impressed by Ecuador’s president and his ministers who are educated, ethical and philosophical people … who truly and honestly investigated the claims made by my son,” she told AAP.