LONDON - Julian Assange, founder of the WikiLeaks website, was arrested here Tuesday and ordered to remain in custody until a hearing next week on extraditing him to Sweden, where he is wanted for questioning over allegations of sexual assault.

The Obama administration also is mulling ways to prosecute Assange for WikiLeaks' publication of a torrent of confidential U.S. diplomatic and Pentagon files.

Attorney General Eric H. Holder Jr. said this week that prosecutors had "other tools we have at our disposal" besides filing espionage charges. Among them, according to law enforcement sources, is charging Assange with receiving stolen property.

Any such proceedings would set up a test of whether the First Amendment's protection for a free press extends to a website with a worldwide audience.

The detention of Assange in London came as governments and businesses around the world continued their efforts to halt the ability of WikiLeaks to function.

On Tuesday, a Visa Europe spokesman said the firm was suspending its business with WikiLeaks, following in the footsteps of Amazon.com, MasterCard, the online pay service PayPal, and others.

Assange's lawyer, Mark Stephens, called his client innocent of any sex charges and questioned whether the accusations were part of an effort by governments to silence him.

"Many people believe Mr. Assange to be innocent, myself included," he said. "Many people believe the prosecution to be politically motivated."

Assange, 39, turned himself in to police Tuesday morning, hours after Britain received a formal warrant for his arrest from Swedish authorities. Assange denies any wrongdoing and says he will fight the attempt to extradite him, beginning with a hearing next Tuesday.

That could be the start of a legal battle that could drag on for weeks or even months, in part because the case against him in Sweden remains murky.

Assange, who is Australian, is eager to avoid extradition for fear that it could set the stage for him to be sent to the United States.

Those leaked files have turned Assange into an international figure, vilified by governments for spilling official secrets while lionized by activists demanding a free flow of information.

The ability of WikiLeaks to raise money and release information is being hemmed in as the businesses it relies on to operate terminate their relationships, saying the organization's actions are in violation of customer agreements.

A PayPal spokesman said a U.S. State Department letter Nov. 27, which termed as illegal WikiLeaks' dissemination of the American diplomatic cables, "triggered a review" of a fund-raising account on the WikiLeaks website.

While businesses can act on their own, the U.S. government faces a high legal hurdle in trying to shut down the site through court action, said Marcia Hoffman, senior staff attorney for the electronic Frontier Foundation.

A spokesman for WikiLeaks vowed that Assange's arrest would not affect the website's plans to continue publishing its cache of confidential documents.

Among WikiLeaks' strategies to keep its content available is so-called mirroring - copying its files and documents to scores of other sites around the Web. As of Tuesday morning, WikiLeaks listed 755 mirror sites, more than twice as many as it said it had just two days earlier.

The sex accusations against Assange in Sweden have dogged him since the summer, before his organization began releasing portions of its huge trove of rifled State Department cables.

The allegations stem from separate liaisons he had with two women in August, which Swedish prosecutors say may have involved molestation, "unlawful coercion," and rape.

Assange insists that the encounters were consensual.

In a packed London courtroom, Assange refused voluntary extradition to Sweden and asked to be freed on bail.

Prosecutors objected, saying Assange's nomadic lifestyle made him a flight risk. They noted that he first gave the court only a post-office box as an address and, when that was disallowed, a street address in Victoria state in his native Australia.