Britain's Supreme Court ruled Wednesday that WikiLeaks founder Julian Assange can be extradited to Sweden, but put his deportation on hold to give his lawyers a final chance to reopen the case.

The court, which handed down its decision after an 18-month legal marathon, rejected Assange's argument that the Swedish prosecutor who issued the arrest warrant over sex crime allegations was not entitled to do so.

"The request for Mr Assange's extradition has been lawfully made and his appeal against extradition is accordingly dismissed," Supreme Court president Nicholas Phillips said as he delivered the ruling to a hushed courtroom.

The seven judges were split five to two but their majority ruling was that the prosecutor was a rightful judicial authority, and therefore allowed to issue the warrant for the Internet whistleblower.

But in a new twist, Assange's lawyer Dinah Rose asked for 14 days to consider whether to apply to reopen the case, on the grounds that the judgment referred to material that was not mentioned during the last hearing in February.

The judge granted the request wholesale ray bans, which is highly unusual in the three-year history of the Supreme Court.

"With the agreement of the respondent, the required period for extradition shall not commence until 13th June 2012," the Supreme Court said in a statement.

Assange, a 40-year-old Australian national, was not in the central London court for the judgement. One of his supporters, journalist John Pilger, said he was "stuck in traffic" with his mother, who flew in from Australia for the verdict.

The Swedish lawyer for the two women who accuse Assange of rape and sexual assault said he would be extradited eventually.

"The decision was what we expected... It's unfortunate that it has been delayed further, but he will ultimately be extradited," Claes Borgstroem told AFP.

Assange is at present wanted for questioning over the sex crime allegations, but Borgstroem said he expected an indictment perhaps within a month after he gets to Sweden.

Australia said it would closely monitor the case and added that consular officials were available to help him if he wished.

"The Australian government cannot interfere in the judicial processes of other governments but we will closely monitor the proceedings against Mr Assange in Sweden," said a spokeswoman for Australia's Department of Foreign Affairs.

Assange, whose website enraged Washington by releasing a flood of state and military secrets, has been living under tight restrictions on his movement for 540 days, including wearing an ankle tag and reporting daily to police.

He has said he fears his extradition would eventually lead to his transfer to the United States, where US soldier Bradley Manning is facing a court-martial over accusations that he handed documents to WikiLeaks.

Outside court, Assange's principal lawyer Gareth Peirce confirmed that the extradition was stayed while his legal team considers whether to apply to reopen the case, although the judgement still stands.

The point in question is the interpretation of the Vienna Convention on the law of treaties, "which was never addressed in the hearing, one way or another, by either side," Peirce added.

If Assange fails to have the case reopened in Britain, he still has the option of a last-ditch appeal to the European Court of Human Rights in Strasbourg.

The white-haired Assange does not deny that he had sex with two WikiLeaks volunteers in Sweden while attending a WikiLeaks seminar cheap ray bans, but insists the sex was consensual and argues there are political motives behind the attempts to extradite him.

Assange's mother Christine told Australian television ahead of the judgement: "It's a 24-hour nightmare because we know he is not safe and the biggest governments in the world are gunning for him."

The former computer hacker has been fighting deportation since his arrest in London in December 2010 on the European arrest warrant issued by Sweden.

The Supreme Court is his final avenue of appeal under British law, after two lower courts ruled he should be sent to Sweden for questioning.