Skirmishes raged across cyberspace Thursday between WikiLeaks supporters and the companies they accuse of trying to stifle the whistleblower website, with both sides taking hits.

UN High Commissioner for Human Rights Navi Pillay speaks during a press conference in Geneva. Pillay says she is concerned about reports of pressure on payment providers such as MasterCard to stop processing donations to WikiLeaks. (Anja Niedringhaus/Associated Press)

The UN's top human rights official raised the alarm over officials' and corporations' moves to cut off WikiLeaks funding and deny it server space. Navi Pillay described such actions as "potentially violating WikiLeaks's right to freedom of expression."

She also expressed surprise at the scale of the online attacks by WikiLeaks supporters that have targeted major U.S. financial players such as MasterCard and Visa — in some cases rendering their websites inaccessible for hours at a time.

"It's truly what media would call a cyberwar," Pillay told reporters in Geneva. "It's just astonishing what is happening."

WikiLeaks has been under intense pressure since it began publishing some of the 250,000 leaked U.S. diplomatic cables it obtained. There have been attacks on its website and threats against its co-founder, Julian Assange, who is now in a British jail fighting extradition to Sweden on charges of sexual assault against two women.

The cables date from 1966 to February 2010 and contain confidential communications between 274 embassies in countries throughout the world and the U.S. State Department; 15,652 of the cables are classified as secret.

WikiLeaks has said it intends to release them in stages, and as of Thursday evening, had released about 1,200 of them. The first batch of cables was released in conjunction with several major media outlets, namely, the Guardian, the New York Times, El Pais, Der Spiegel and Le Monde.

Prior to the publication of the cables, journalists at those media organizations advised WikiLeaks on which of the cables should be released and what details and names should be withheld from the published documents.

Brazilian president surprised by lack of outcry

U.S. officials say WikiLeaks's actions have thrown diplomacy into disarray, caused countries to curtail dealings with the U.S. and, in the case of an earlier WikiLeaks release of classified military documents, put the lives of informants at risk.

While U.S. allies have also criticized WikiLeaks, some world leaders have questioned the arrest of Assange.

Russian Prime Minister Vladimir Putin, questioning the reliability of leaked U.S. cables referring to his nation as undemocratic and corrupt, said the fact that Assange is in custody shows the West has its own problems with democracy.

"Why was Mr. Assange hidden in prison?" Putin asked at a news conference. "Is this democracy?"

'There is [no protest] … for freedom of expression and against the imprisonment of this guy who was doing better work than many of the ambassadors.'—Luiz Inacio Lula da Silva, Brazilian president

Brazilian President Luiz Inacio Lula da Silva said he was surprised by the lack of outcry against Assange's arrest.

"This WikiLeaks guy was arrested, and I'm not seeing any protest for freedom of expression," Silva said Thursday in Brasilia.

"There is nothing, nothing for freedom of expression and against the imprisonment of this guy who was doing better work than many of the ambassadors."

Many U.S.-based internet companies have cut their ties to WikiLeaks under pressure form the U.S. government. They include MasterCard, Visa, PayPal, EveryDNS and Amazon Web Services, the web hosting arm of Amazon.com.

Those moves have hurt WikiLeaks's ability to accept donations and publishing content and touched off a bout of web-based warfare.

Hundreds of people have set up mirror sites to host WikiLeaks content, and a group of "hacktivists" using the handle "Anonymous" have launched a series of retaliatory attacks — which WikiLeaks says it does not sanction — against the companies that have cut ties with WikiLeaks.

In the Netherlands, a 16-year-old boy suspected of being involved in the digital attacks on PayPal, MasterCard and other sites was arrested Thursday.