WikiLeaks founder Julian Assange was denied bail on Wednesday because a judge said there is a risk he may abscond while the United States tries to secure his extradition from Britain.
Assange has spent more than eight years either holed up in the London's Ecuadorean embassy or in jail.
But Assange on Monday won an attempt to stop his extradition to the United States to face 18 criminal charges of breaking an espionage law and conspiring to hack government computers. He had then asked to be bailed.
"I am satisfied that there are substantial grounds for believing that if Mr Assange is released today he would fail to surrender to court to face the appeal proceedings," Judge Vanessa Baraitser said.
The US Department of Justice says it will continue to seek Assange's extradition.
"As far as Mr Assange is concerned this case has not yet been won... the outcome of this appeal is not yet known," Baraitser said.
Admirers hail Australian-born Assange as a hero for exposing what they describe as abuses of power by the United States. But detractors cast him as a dangerous figure who has undermined the security of the West, and dispute that he is a journalist.
WikiLeaks published hundreds of thousands of secret US diplomatic cables that laid bare often critical US appraisals of world leaders, from Russian President Vladimir Putin to members of the Saudi royal family.
Assange made international headlines in early 2010 when WikiLeaks published a classified US military video showing a 2007 attack by Apache helicopters that killed a dozen people in Baghdad, including two Reuters news staff.