LONDON, UK (AFP) – WikiLeaks founder Julian Assange will have to remain in custody in Britain, pending a US appeal of the decision to block his extradition to face charges for leaking secret documents, a judge in London ruled Wednesday.

Judge Vanessa Baraitser told Westminster Magistrates Court there were “substantial grounds for believing that if Mr Assange is released today he will fail to surrender” for the appeal hearings.

“Mr Assange still has an incentive to abscond from these as yet unresolved proceedings,” she said.

“As a matter of fairness the United States must be able to challenge my decision. If Mr Assange absconds during this process then they will have lost the opportunity to do so.”

The US had earlier urged Baraitser not to release the 49-year-old, while it prepares to challenge Baraitser’s decision on mental health grounds to block his extradition to face charges for publishing secret documents.

Lawyer Clair Dobbin, representing the government in Washington, told the court there were “no conditions that could guarantee his surrender” if he were freed from custody.

“The history of his attempts to evade extradition to the United States demonstrated that he is capable of going to any length to avoid that possibility,” she added.

Assange was in court to hear the application and ruling, two days after an unexpected decision Monday to block his removal to the United States on the grounds he was a suicide risk.

Dobbin said the court “should be under no doubt about his resources to abscond”, pointing to his previous flouting of bail conditions, and an offer of political asylum, notably from Mexico.

But Assange’s lawyer, Edward Fitzgerald, said he should be freed, after spending 15 months in custody awaiting the extradition proceedings.

“We say after all this time, after the long proceedings over a year… the court has given a decision and the decision has been that he should be discharged,” he added.