Wikileaks founder Julian Assange is seeking political asylum at Ecuador's London embassy, the country's foreign minister has said.
"Ecuador is studying and analysing the request," Foreign Minister Ricardo Patino told reporters in Quito.
Last week the UK's Supreme Court dismissed Mr Assange's bid to reopen an appeal against extradition to Sweden over alleged sex crimes he denies.
The Foreign Office says it will work with Ecuador to resolve the situation.
Mr Assange could still take his case against extradition to the ECHR and has until 28 June to make the move, or extradition proceedings will begin.
Swedish prosecutors want to question him over allegations of rape and sexual assault made by two female former Wikileaks volunteers in mid-2010 but have not filed any charges.
Mr Assange, whose Wikileaks website has published a mass of leaked diplomatic cables that embarrassed several governments and international businesses, claims the sex was consensual.
'Minimum guarantees'In a statement, Ecuador's embassy said he had arrived there on Tuesday afternoon to seek asylum.
"As a signatory to the United Nations Universal Declaration for Human Rights, with an obligation to review all applications for asylum, we have immediately passed his application on to the relevant department in Quito," it said.
"While the department assesses Mr Assange's application, Mr Assange will remain at the embassy, under the protection of the Ecuadorean government."
It said the decision to consider the bid for asylum "should in no way be interpreted as the government of Ecuador interfering in the judicial processes of either the United Kingdom or Sweden."
Mr Assange issued a statement, saying he was "grateful to the Ecuadorean ambassador and the government of Ecuador for considering my application".
Associated Press quoted Mr Patino as telling reporters Mr Assange had written to Ecuadorean President Rafael Correa saying he was being persecuted.
Mr Patino said the Australian had claimed "the authorities in his country" would not "defend his minimum guarantees in front of any government".
Mr Assange said he would not be protected from being extradited to "a foreign country that applies the death penalty for the crime of espionage and sedition," Mr Patino said.
The Foreign Office said the UK had now been officially informed by the authorities in Ecuador that Julian Assange was seeking asylum.
Since he was now in the embassy of Ecuador, he was "on diplomatic territory and beyond the reach of the police," a spokesman said.
The anti-secrecy campaigner fears extradition to Sweden may lead to him being sent to the US to face separate charges relating to Wikileaks, for which he could face the death penalty.
But Swedish authorities have said the European Court of Human Rights (ECHR) would intervene if Mr Assange was to face the prospect of "inhuman or degrading treatment or an unfair trial" in the US.
Mr Assange was on £200,000 bail which was provided by several high-profile supporters including socialite Jemima Khan and Ken Loach, who each offered £20,000 as surety.
Ms Khan said on Twitter that she had expected him to face the allegations, adding, "I am as surprised as anyone by this".
Vaughan Smith, a friend who allowed Mr Assange to stay at his Norfolk home until December 2011, told the BBC he was surprised by the move but understood why he may have decided to seek asylum.
"There's been an organised campaign to undermine him," Mr Smith said. "And he believed that if he was sent to Sweden he would be sent to America."
Wikileaks has posted an alert on its Twitter feed: "ALERT: Julian Assange has requested political asylum and is under the protection of the Ecuadorian embassy in London."
It said Ecuador had offered asylum as early as November 2010.
Ecuador's deputy foreign minister said in 2010 his country was offering Mr Assange residency because it wanted to give him the opportunity to freely present the information he had.
However, President Rafael Correa subsequently dismissed the idea, which he said neither he nor Mr Patino had approved.
Source: BBC News