Wikileaks website founder Julian Assange is in Britain and police know his whereabouts but have refrained so far from acting on an international warrant for his arrest, a British newspaper said on Thursday.

Julian Assange, founder of whistle-blowing website WikiLeaks, holds a news conference at the Geneva Press Club in Geneva in this Nov 4, 2010 file photo. Interpol issued a "red notice" on Nov 30, 2010 to assist in the arrest of Assange, who is wanted in Sweden on suspicion of sexual crimes.

The 39-year-old Australian, who founded the whistle-blowing website that has disclosed a trove of secret US diplomatic cables, supplied British police with contact details upon his arrival in October, The Independent said.

The newspaper cited police sources who said they knew where Assange was staying and had his telephone number. It added that it was believed he was in southeast England.

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The international police agency Interpol this week issued a "red notice" to assist in the arrest of Assange, who is wanted in Sweden on suspicion of sexual crimes, but Britain's Serious Organised Crime Agency (Soca) so far has refused to authorise this, the paper said.

Citing unnamed sources, the Independent said Soca needed clarifications about the European Arrest Warrant issued by Swedish prosecutors but it described the delay as technical.

The Metropolitan Police and Soca declined to comment when contacted by Reuters.

Assange, a former computer hacker, leads a nomadic existence and cultivates an aura of mystery. He left Sweden last month after authorities there said they wanted to question him about allegations of rape and other sexual offenses.

US authorities, bruised by the international damage caused by thousands of classified US documents being leaked to the media, have promised to take action to shut down such activities.

On Monday, US Attorney General Eric Holder said the Justice Department had "an active, ongoing criminal investigation with regard to this matter" and insisted the Obama administration's promises of action were "not saber rattling".