A court in Britain granted WikiLeaks founder Julian Assange bail but lawyers acting for Swedish authorities immediately said they would challenge the decision.
Mr Assange denies allegations that he sexually assaulted two women in Sweden, and is fighting attempts to extradite him.
The lawyer announced at a court hearing the decision to challenge bail, without giving reasons.
The judge, who had earlier granted Mr Assange bail under stringent conditions, said the 39-year-old Australian must remain in custody until the appeal is heard within 48 hours.
The bail conditions required sureties amounting to £240,000, a curfew and the wearing of an electronic tag.
Mr Assange was refused bail last week despite the offer of sureties from figures including film director Ken Loach, the BBC reports.
Julian Assange, whose website has provoked US fury by publishing some of the 250,000 classified US diplomatic papers it has obtained, was accused this year of sexual misconduct by two WikiLeaks volunteers during a stay in Sweden.