WikiLeaks founder Julian Assange has launched an appeal against a ruling that he should be extradited from Britain to Sweden over alleged sex crimes, his lawyer said on Thursday.

Last week Assange, who infuriated the US government by publishing thousands of secret US diplomatic cables, was told by a British judge he could be sent to Sweden to face questioning over complaints by two female WikiLeaks volunteers.

The 39-year-old Australian computer expert vowed to fight the extradition decision and his lawyers have now lodged papers appealing the verdict at London's High Court.

One volunteer accuses Assange of sexually molesting her by ignoring her request for him to use a condom during sex; the second says he had sex with her while she was asleep and that he was not wearing a condom, an allegation which falls into the least severe of three rape categories in Sweden.

Assange's lawyers claim he will not get a fair trial in Sweden, as rape cases are held in secret. They criticise the European arrest warrant system used to seek his extradition, and say there are political motivations for the prosecution.

"Those are issues that should concern any right-thinking person and the question will come to whether we should be sending people to countries which don't respect minimum human rights standards," Assange's lawyer Mark Stephens told Reuters.

WikiLeaks caused a media and diplomatic uproar late last year when it began to publish its cache of more than 250,000 US diplomatic cables, revealing secrets such as that Saudi leaders had urged US military action against Iran.

On Wednesday, the US military said it had brought 22 new charges against the soldier accused of leaking the sensitive documents and US prosecutors are looking at where charges can be brought against Assange.

After last week's verdict Assange, who is currently free under strict bail conditions, accused the United States of putting pressure on Britain, Sweden and the media.

Stephens said his appeal case was likely to be heard in the next two to three months and if unsuccessful, permission could ultimately be granted for a challenge to the country's top judges in the Supreme Court who can rule on points of law.

"In any ordinary case it would be granted but of course we are dealing with Julian Assange," Stephens said. "This case has been thus far fast-tracked in a way which is unusual."