(AFP) - Julian Assange remained holed up in Ecuador's London embassy Friday with police guarding its exits, after Britain warned that a diplomatic standoff over the WikiLeaks founder could go on for years.

Ecuador on Thursday granted asylum to Assange -- whose website enraged the United States by publishing a vast cache of confidential government files -- but Britain has vowed not to grant him safe passage out of the country.

British Foreign Secretary William Hague said his government was obliged under its own laws to extradite the Australian national to Sweden, where he is wanted for questioning over alleged sex crimes.

"No one, least of all the government of Ecuador, should be in any doubt that we are determined to carry out our legal obligation to see Mr Assange extradited to Sweden," Hague told a press conference.

The Organisation of American States on Friday called a meeting of foreign ministers for August 24 to discuss the standoff.

Twenty-three countries voted for the resolution proposed by Ecuador to convene the meeting at its Washington headquarters. The United States, Canada and Trinidad and Tobago voted no.

The vote was taken at emergency talks to discuss the Assange case after Ecuador turned to the OAS for help.

The US envoy to the OAS, Carmen Lomellin, said a meeting of OAS foreign ministers "would be unhelpful and harmful to the OAS' reputation as an institution".

Ecuador wants the body to discuss Britain's threat to storm its embassy by force to take Assange into custody.

Under a 1954 agreement, the OAS agreed to allow asylum in diplomatic missions for "persons being sought for political reasons", although not individuals indicted for "common offenses".

The United States said earlier Friday it does not believe in the concept of "diplomatic asylum".

"We believe this is a bilateral issue between Ecuador and the United Kingdom and that the OAS has no role to play in this matter," the State Department said in a statement.

Meanwhile, both Ecuador and Sweden suggested Friday they were prepared to be patient and wait.

Ecuador's President Rafael Correa said Assange will remain in Quito's embassy as long as Britain refuses to give him safe passage.

"The problem is that they aren't going to give him the safe conduct," Correa said in a radio interview, adding that "Mr Assange can stay indefinitely in our embassy".

Swedish Foreign Minister Carl Bildt told Sweden's TT news agency: "We have no reason to do too much, we're going to wait and see what happens."

Some 20 British police were stationed outside the embassy Friday, ready to arrest the 41-year-old Assange if he leaves the premises.

WikiLeaks condemned the police presence as "intimidation tactics".

A handful of supporters of the former computer hacker camped overnight outside the embassy in London's plush Knightsbridge district in a bid to "guard" Assange against any potential attempt to arrest him.

"We'll stay here as long as we have to," 26-year-old protester Baba Gena told AFP.

A couple of activists brought a megaphone along and yelled at police: "Why aren't you doing your job properly?" and "Put your hands in the air if you believe in freedom of speech!"

Assange has not left the embassy since June 19, when he walked in and asked for asylum.

WikiLeaks said on Twitter that he would give a statement in front of the embassy on Sunday, though it did not specify whether this would involve leaving the premises and, if so, how he would do so without being arrested.

Under normal diplomatic procedures, embassies are considered the territory of the countries they represent and cannot be entered without permission.

Britain has angered Ecuador by suggesting it could invoke the Diplomatic and Consular Premises Act of 1987, which it says allows it to revoke the diplomatic immunity of an embassy on British soil and go in to arrest Assange.

But Philip Barton, Britain's envoy to the OAS as an observer, said: "Allegations that the UK was threatening Ecuador and about to storm the embassy are without foundation".

Baltasar Garzon, the renowned Spanish lawyer who is helping Assange's defence, has said the WikiLeaks founder will appeal to the International Court of Justice if Britain does not backtrack and guarantee him safe passage.

WikiLeaks spokesman Kristinn Hrafnsson told AFP that any bid to enter the embassy would "risk upsetting diplomatic relations all over the world".

A Foreign Office spokesman said Friday that Britain was "committed to working with the Ecuadorans to solve this matter amicably".

In 2010, WikiLeaks published hundreds of thousands of US military documents on the war in Iraq and Afghanistan, as well as diplomatic cables that deeply embarrassed Washington.

Supporters fear Assange could face the death penalty if he were to be sent to the United States and tried on espionage charges.