Britain's Supreme Court said on Thursday it has rejected an application by WikiLeaks founder Julian Assange to reopen his appeal against extradition to Sweden.

"The Supreme Court of the United Kingdom has dismissed the application made by Ms Dinah Rose QC, counsel for Mr Julian Assange, seeking to reopen their appeal," the court said in a statement.

Seven Supreme Court justices unanimously dismissed the move by Assange's lawyers as being "without merit".

The court added that the 40-year-old Australian behind the whistleblowing website could not be extradited for at least two weeks.

"In addition, the Court has ordered that... the required period for extradition shall not commence until the 14th day after today," it said.

The Supreme Court last month rejected Assange's appeal against extradition to Sweden, where he is wanted for questioning about allegations of rape and sexual assault.

The court, Britain's highest, handed down its decision in the 18-month legal marathon after rejecting Assange's argument that the Swedish prosecutor who issued the arrest warrant for him was not entitled to do so.

But in a surprise move, Assange's lawyer asked for 14 days to consider whether to apply to reopen the case, on the grounds that the judgment referred to material not mentioned during the appeal hearing in February.

[Wikileaks founder Julian Assange in London in February. AFP Photo/Miguel Medina]