The Swedish prosecutor heading an investigation into a rape allegation against WikiLeaks founder Julian Assange has filed a request for his arrest, the Prosecution Authority said.

The warrant, if granted, would be the first step in a process to have Assange extradited from Britain, where he is serving a 50-week sentence for skipping bail.

"I request the District Court to detain Assange in his absence, on probable cause suspected for rape," Deputy Chief Prosecutor Eva-Marie Persson said in a statement.

She said she would issue a European arrest warrant for Assange to be surrendered to Sweden if the court decided to detain him.

Sweden reopened an investigation into the rape allegation, first made in 2010, on 13 May when Ms Persson said she would continue a preliminary investigation that was dropped in 2017 without charges being brought, after Assange took refuge in the Ecuadorian embassy in London.

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Assange, who denies the accusation, was arrested in Britain last month after spending seven years hiding inside the embassy.

The Swedish prosecutor said she would request Assange be detained in his absence on probable cause for an allegation of rape and that her office would issue a European arrest warrant - the start of the extradition process.

The United States is also seeking to extradite him on conspiracy charges relating to the public release by Wikileaks of a cache of secret documents, including assessments of foreign leaders, wars and security matters.

The British courts will have to rule on the two extradition requests, with Home Secretary Sajid Javid having the final say on which one takes precedence.

A British judge has given the US government a deadline of 12 June to outline its case against Assange.

The statute of limitation for rape in Sweden is ten years - a deadline which would be reached in mid-August next year for that alleged incident, leaving prosecutors pressed for time should they decide to file any formal charge.

Ms Persson said she would request to interview Assange while he was in British custody, but that this would require the consent of the Australian, who fought unsuccesfully through the British courts to avoid extradition before fleeing to the embassy.