Swedish prosecutors face a hard task of "proving" rape claims against WikiLeaks founder Julian Assange in a climate of mistrust against them, the Swedish Dagens Nyheter newspaper said Friday.

"Once he (Assange) is here (in Sweden), the prosecutor Marianne Ny must expect a thorough examination of the investigation and of the Swedish justice system", which Assange's defence lawyers sought to discredit before the British courts, the newspaper writes.

"The police and the prosecution service will have to act more intelligently than they have done" to date, it said, suggesting that investigators use "a working tape recorder when questioning" Assange.

British judge Howard Riddle ruled Thursday that Assange can be extradited to Sweden to face rape charges there.

The Australian former computer former hacker strongly denies the claims, insisting the extradition attempt is politically motivated and stems from WikiLeaks' release of thousands of classified US cables.

His lawyers strongly criticised the Swedish justice system during the extradition hearing, attacking the practice of holding rape trials behind closed doors, and claiming that Sweden has excessively strict sexual assault laws.

Assange, who said he would appeal the decision, fears that Sweden will deliver him to the United States, where some politicians have called for him to face the death penalty for leaking state secrets.

"The question that arises now is whether the United States will seek Mr Assange's extradition," wrote the Dagens Nyheter.

The tabloid Aftonbladet said lawyers were the only beneficiaries of the lengthy legal battle.

"It would have been easier and cheaper for Assange to have taken a plane to Sweden to answer the prosecutor's questions," the country's biggest selling daily wrote.