WikiLeaks founder Julian Assange was remanded in custody until 14 December by a London court on Tuesday after saying he would fight his extradition to Sweden on suspicion of rape and molestation.
The 39-year-old Australian, whose whistleblowing website has enraged Washington by releasing thousands of secret US diplomatic cables, appeared in court just hours after handing himself in to British police.
Filmmaker Ken Loach, socialite Jemima Khan and campaigning journalist John Pilger each offered £20,000 (€23,600, $31,400) for Assange's bail, but it was refused on the grounds that he might try to flee Britain.
"These are extremely serious allegations," district judge Howard Riddle said at City of Westminster magistrates court, adding that Assange faced alleged sexual offences against two women.
"I am satisfied that there are substantial grounds to believe that if granted bail he would fail to surrender," the judge added.
The judge said Assange had "comparatively weak community ties in this country" and had the "means and ability to abscond if he wants to."
Assange appeared calm in court, an AFP reporter said. Wearing a navy blue suit and a white shirt without a tie, he spoke to confirm his name and address, giving an Australian PO box address.
When pressed by the judge he gave another address in Victoria, Australia.
The former hacker denies the Swedish claims. He says they stem from a dispute over consensual, unprotected sex with two women and that the accusations may be politically motivated.
WikiLeaks vowed that the detention of its founder would not stop it releasing more of the confidential US cables.
"Today's actions against our editor-in-chief Julian Assange won't affect our operations: we will release more cables tonight as normal," it said in a statement on Twitter.
James Ball, a WikiLeaks journalist in London, told AFP that staff were working "on schedule, all that stuff will keep rolling out as ever".
In a sign of Washington's satisfaction at the arrest, US Defence Secretary Robert Gates, who was visiting Afghanistan on Tuesday, said it "sounds like good news."
Britain's Metropolitan Police said earlier in a statement that officers from its extradition unit had arrested Assange on a European arrest warrant "by appointment at a London police station" at 0930 GMT.
"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 police statement said.
The arrest of Assange comes as a fresh blow to WikiLeaks, which has been chased around the globe since it started to release a cache of 250,000 US diplomatic memos on 28 November.
The website has hopped from server to server as various countries tried to close it down, even as its supporters have responded by setting up hundreds of "mirror" sites to keep it online.
WikiLeaks is also coming under increased financial pressure, with Visa following in the footsteps of MasterCard and PayPal Tuesday by announcing that it was suspending all payments to WikiLeaks.
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.
WikiLeaks has already been expelled from the United States where the US Attorney General Eric Holder has said authorities were pursuing an "active, ongoing investigation that is criminal in nature," into the leaks.
US politicians have called for Assange to be treated as a terrorist.
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.