Informal discussions have already been held between American and Swedish officials about the possibility of WikiLeaks founder Julian Assange eventually being delivered into United States custody, according to diplomatic sources.

Assange, 39, was in a British jail last night awaiting extradition to Sweden, where he is wanted over allegations that he sexually assaulted two women. The Australian was refused bail at City of Westminster magistrates' court on the grounds there was a risk he would abscond, despite a number of prominent public figures offering sureties.

His arrest was described by the US Defence Secretary, Robert Gates, as "good news". The US Justice Department is considering charging Assange with espionage offences after his website released classified US diplomatic files.

Assange's appearance in the London court put Britain at the centre of the controversy and recrimination over the publication of thousands of diplomatic cables that have caused acute embarrassment to the US Administration.

If the whistle-blower responsible for putting them in the public domain is to be silenced, his supporters say, the process began in London.

The Swedish Government is seeking to extradite Assange over alleged sex offences involving two women. Sources stressed that no extradition request from Washington would be considered unless the US Government laid charges against Assange, and that attempts to send him to America would take place only after legal proceedings were concluded in Sweden.

Assange went voluntarily to a London police station, accompanied by solicitors, after an international warrant was issued. The court heard that film director Ken Loach, journalist John Pilger and Jemima Khan, the sister of Tory MP Zac Goldsmith, were among those offering to stand bail to the sum of £180,000 ($376,000). But District Judge Howard Riddle remanded Assange in custody until next week, saying there was a risk he might try to flee.

Loach, who offered to contribute £20,000, explained that he did not know Assange other than by reputation, but said: "I think the work he has done has been a public service. I think we are entitled to know the dealings of those that govern us."

Pilger, who also offered £20,000, said he knew Assange as a journalist and personal friend and had a "very high regard for him.

He said: "I am aware of the offences and I am also aware of quite a lot of the detail around the offences."

"I am here today because the charges against him in Sweden are absurd and were judged as absurd by the chief prosecutor there when she threw the whole thing out until a senior political figure intervened."

Khan offered a further £20,000 "or more if need be", although she said she did not know Assange.

Gemma Lindfield, appearing for the Swedish authorities, said she opposed bail because there was a risk Assange would fail to surrender - and also for his own protection. She outlined five reasons why there was a risk: his "nomadic" lifestyle, reports that he intended to seek asylum in Switzerland, access to money from donors, his global network of contacts and his Australian nationality.

Lindfield added: "Any number of people could take it upon themselves to cause him harm. This is someone for whom, simply put, there is no condition, even the most stringent, that would ensure he would surrender to the jurisdiction of this court."

Lindfield said Assange was wanted over four alleged sex offences. One potential charge is that he had unprotected sex with a woman, identified only as Miss A, when she insisted he use a condom. Another is that he had unprotected sex with another woman, Miss W, while she was asleep.

Judge Riddle said: "This case is not, on the face of it, about WikiLeaks. It is an allegation in another European country of serious sexual offences ... involving two separate victims ... It seems to me that if these allegations are true, then no one could argue the defendant should be granted bail."

However, he added: "If they are false, he suffers a great injustice if he is remanded in custody. At this stage, the nature and strength of the allegations is not known."

Assange's solicitor, John Jones, said: "Mr Assange has made repeated requests that the allegations against him be communicated to him in a language he understands. That has been ignored by the Swedish prosecutor. Another Swedish prosecutor dropped this case early on for lack of evidence."

The pressure on WikiLeaks, which relies on online donations, continued after Visa and Mastercard suspended payments to its website.