British Home Secretary Sajid Javid has received an extradition request to send Julian Assange to the United States.
Mr Javid earlier told the BBC he had signed the order, however, the British Home Office says he certified it and that the final decision on Assange's extradition would be up to the court.
"The Home Secretary must certify a valid request for extradition … unless certain narrow exceptions in section 70 of the Extradition Act 2003 apply," a Home Office spokesman said in a statement.
"It's a decision ultimately for the courts … I want to see justice done and we have a legitimate extradition request," Mr Javid said.
Assange's lawyer Jennifer Robinson told the ABC the certifying of the order was a normal part of the process and the extradition challenge now begins.
Assange wanted in US and Sweden
Assange, who is currently serving a 50-week jail sentence for skipping bail, is due to face court in London on Friday for the extradition hearing.
The United States has charged him with conspiracy to commit computer intrusion, which carries a maximum penalty of five years in prison.
US government counsel Ben Brandon previously told the Westminster Magistrates' Court the case against Assange involved one of the biggest compromises of classified information in history.
It included hundreds of thousands of activity reports relating to the Afghanistan and Iraq wars and 250,000 US diplomatic cables.
He is accused of conspiring with former US Army intelligence analyst Chelsea Manning to crack passwords to gain access to the information, which was subsequently posted on WikiLeaks.
Sweden has also reopened its own investigation into a 2010 rape allegation made against the WikiLeaks founder.
Earlier this month, the Uppsala District Court rejected a request from prosecutors to detain him in absentia.
However, the ruling does not mean the preliminary rape investigation must be abandoned, only that Assange won't be extradited to Sweden for now.
Assange was arrested by British police and carried from the Ecuadorean embassy after his South American hosts abruptly revoked his seven-year asylum in April.