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U.S. Secretary of State Hillary Clinton gestures as she delivers a statement about WikiLeaks at the State Department in Washington on Monday. ((Yuri Gripas/Reuters) )

The United States believes its ally, Saudi Arabia, is ineffective at stopping terrorist fundraising in its own country, according to a cable obtained by WikiLeaks and published by the New York Times and the Guardian.

"It has been an ongoing challenge to persuade Saudi officials to treat terrorist financing from Saudi Arabia as a strategic priority," U.S. Secretary of State Hillary Clinton wrote in a cable on Dec. 30, 2009.

In the same cable, Clinton pointed to donors in Saudi Arabia as the "most significant source of funding to Sunni terrorist groups worldwide."

Such candid remarks had never been made public before  the release of diplomatic cables between the U.S. State Department and its embassies and consulates around the world by WikiLeaks. The whistle-blowing website began releasing cables Nov. 28 and plans to publish 251,287 reports in the coming days.

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Julian Assange, founder of WikiLeaks, holds a news conference in Geneva on Nov. 4. ((Reuters/Valentin Flauraud))

The latest embarrassment for the U.S. fuelled more Republican calls to stop Julian Assange, the editor in chief and public face of WikiLeaks.

"He has done extreme damage to our country and I think he needs to be prosecuted to the fullest extent of the law," said Senate Republican leader Mitch McConnell said.

Meanwhile, WikiLeaks was forced to switch domain names after its U.S. host blocked the site. It is still reachable at the IP address http://213.251.145.96 from a provider in France.

Assange's lawyer in Britain said his client is holding back some sensitive material about the BP oil spill and Guantanamo Bay, which could be released if anything happens to the website or to him.

"They have been subject to a lot of cyber attacks, they've been subject to censorship around the world and they need to protect themselves and this is what they believe to be a thermo-nuclear device effectively in the electronic age,"  Mark Stephens told the BBC.

Assange is facing death threats and allegations of sexual misconduct by two WikiLeaks volunteers in Sweden. He has denied any wrongdoing and no charges have been laid.

His lawyer alleges that the case being prepared against Assange in Sweden is politically motivated.

The search for Assange stepped up on Wednesday as Sweden confirmed it issued a European arrest warrant for him. Since leaving Sweden, Assange has appeared in Britain and Switzerland but disappeared from public view after a Nov. 5 news conference in Geneva.

He has spoken publicly only through online interviews, and WikiLeaks spokesman Kristinn Hrafnsson said late Wednesday the organization was trying to keep his location, likely somewhere in Britain, a secret for security reasons. He noted commentators in the United States and Canada had called for Assange to be hunted down or killed.

With files from The Associated Press