The elusive 39-year-old Australian was due to appear in court later in the day after surrendering to detectives at a police station in London, setting up an extradition battle that he may have to fight from behind bars.
The United States said the arrest was “good news”, but the whistleblowing website vowed to press ahead with its publication of thousands of US diplomatic cables despite his detention and other attempts to drive it offline.
Britain’s Metropolitan Police said in a statement that officers from its extradition unit had arrested Assange “on behalf of the Swedish authorities on suspicion of rape.”
“Julian Assange… was arrested on a European Arrest Warrant by appointment at a London police station at 09:30hrs,” it said, adding that he was due to appear at the City of Westminster Magistrates court later Tuesday.
“He is accused by the Swedish authorities of one count of unlawful coercion, two counts of sexual molestation and one count of rape, all alleged to have been committed in August 2010.”
The former computer hacker, who last appeared in public in November, denies the Swedish allegations.
He says they stem from a dispute over consensual, unprotected sex with two women and that the accusations may be politically motivated.
And Sunday, Assange’s lawyer Mark Stephens said the hunt for the WikiLeaks boss appeared political.
“I’m really rather worried by the political motivations that appear to be behind this,” he told the British broadcaster.
WikiLeaks itself has been chased around the globe since it started to release the US diplomatic memos on November 28, hopping from server to server as various countries tried to close it down.
In one of the latest leaks, US cables released Tuesday showed that NATO had extended an existing defence plan covering Poland to include Estonia, Latvia and Lithuania after they lobbied for extra protection.
In a statement on Twitter, WikiLeaks said: “Today’s actions against our editor-in-chief Julian Assange won’t affect our operations: we will release more cables tonight as normal.”
A WikiLeaks journalist in London said staff were working as normal.
“In terms of what is happening, all is on schedule, all that stuff will keeping rolling out as ever. That’s all I can tell you,” James Ball, who has been analysing the cables for WikiLeaks, told AFP.
Assange’s lawyers were not immediately available for comment, but they have said he will fight extradition to Sweden, saying they fear he could then be passed on to the United States.
One of his London-based lawyers, Jennifer Robinson, said he was “isolated and persecuted” and that death threats had been made on blogs against Assange’s son.
“I think he will get a fair hearing here in Britain but I think our, his, prospects if he were ever to be returned to the US, which is a real threat, of a fair trial, is, in my view, nigh on impossible,” she told the Australian Broadcasting Corp ahead of his arrest.
A court in Stockholm issued an arrest warrant for Assange on November 18.
Assange could now be embroiled in the extradition process for weeks, or even months. Police sources said Assange was unlikely to be granted bail because of the risk he will try to flee the country.
A spokesman for the London-based Serious Organised Crime Agency (SOCA) told AFP ahead of Assange’s arrest that if he contests his extradition Tuesday there will be a further hearing at which he can argue his case.
If a judge rules he should be sent to Sweden, he would have seven days to appeal and the case could then go all the way to Britain’s Supreme Court. If there is no appeal he would be extradited within 10 days.
US Defence Secretary Robert Gates, who was visiting Afghanistan on Tuesday, said when told about the arrest that it “sounds like good news.”
WikiLeaks has already been expelled from the United States where politicians have called for Assange to be treated as a terrorist. Supporters of the website have
responded by setting up hundreds of “mirror” sites to keep it online.
Swiss authorities shut down one of Assange’s bank accounts on Monday, while a major WikiLeaks donor is in trouble in Germany for not filing its accounts on time.