London ? Skirmishes raged across cyberspace between WikiLeaks supporters and the companies they accuse of trying to stifle the group, with websites on both sides of the battle line taken out of service or choked off by attacks.

The U.N.’s top human rights official raised the alarm Thursday over officials’ and corporations’ moves to cut off WikiLeaks’ funding and starve it of server space — something she described as “potentially violating WikiLeaks’ right to freedom of expression.”

Navi Pillay also expressed surprise at the scale of the online attacks that have targeted major American financial players — in some cases denying access to their websites for hours at a time.

“It’s truly what media would call a cyber-war. It’s just astonishing what is happening,” Pillay told reporters in Geneva.

In the Netherlands, a 16-year-old boy suspected of being involved in digital attacks by Wikileaks supporters was arrested.

U.S. Attorney General Eric Holder said the Justice Department was looking into cyber attacks on opponents of WikiLeaks and companies that have stopped doing business with it. Holder spoke at a news conference following a meeting with European Union law enforcement partners on cybersecurity, counterterrorism and data protection.

WikiLeaks has been under intense pressure since it began publishing some 250,000 secret U.S. diplomatic cables, with attacks on its websites and threats against its founder, Julian Assange, who is now in a British jail fighting extradition to Sweden on sex crime allegations.

U.S. officials say WikiLeaks’ actions have thrown diplomacy into disarray, caused countries to curtail dealings with America and, in the case of an earlier 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.