The noose tightened around the WikiLeaks' founder on Friday as new leaks from the website criticised Britain's military role in Afghanistan and delivered a withering assessment of ex-premier Gordon Brown.

The website itself was killed off the Internet for several hours by massive cyber attacks after Sweden said it would issue a fresh arrest warrant for Julian Assange and US senators vowed to punish him and his organisation. The threat came after damaging new revelations emerged about US criticism of British forces in Afghanistan and a US assessment of former British prime minister Gordon Brown's "abysmal track record."

In a raft of new leaked memos published by the Guardian newspaper Friday senior officials including Afghan President Hamid Karzai criticised British troops for their inability to impose security in the southern province of Helmland.

In a memo sent in April 2007, General Dan McNeill, the then commander of NATO forces in Afghanistan, told a US drug-control officer that he "was particularly dismayed by the British effort.

"They had made a mess of things in Helmand, their tactics were wrong," McNeill said.

In another cable, sent February 21, 2009, a US official says Karzai said the incompetence of British troops had led to a breakdown in law and order in Helmand.

On Gordon Brown, US officials said he had failed to control a "rudderless" Labour party after Tony Blair stepped down in 2007.

A cable sent by then US ambassador Robert Tuttle on July 31, 2008, speculated on the possibility that Brown could be ousted as leader of his party.

"As Gordon Brown lurches from political disaster to disaster, Westminster (the home of Britain's parliament) is abuzz with speculation about whether he will be replaced," the memo began. The cable concluded that because of "Brown's abysmal track record," Labour lawmakers seriously considered staging a coup. Following the latest revelations the WikiLeaks domain name -- wikileaks.org -- was shut down. The website's American domain name system provider, EveryDNS.net, said it took the site offline following reports of massive cyber attacks.

The site was back online six hours later under a different address -- wikileaks.ch hosted in Switzerland. The latest techological setback for the whistleblower site came after Amazon booted it from its computer servers on Wednesday following pressure from US politicians, prompting the site to move to a French server.

Meanwhile the noose appeared to tighten around Assange, after the Supreme Court in Stockholm refused to hear his appeal against an initial warrant over allegations of rape and molestation. Swedish police said they would issue a new warrant as a result of a procedural error in the initial order after police in Britain signalled the mistaker. While Assange has not been seen in public since WikiLeaks began leaking around 250,000 cables on Sunday, his London-based lawyer Mark Stephens denied he was on the run.

"Scotland Yard know where he is, the security services from a number of countries know where he is," Stephens told AFP.

While the elusive whistleblower laid low, a group of US senators introduced legislation that would make it illegal to publish the names of informants serving the US military and intelligence community.

The legislation, which would amend the US Espionage Act aimed at punishing the disclosure of secret information, could help to stop such leaks from happening again. But American legal experts have said the path to prosecution is strewn with potential legal complications, including free speech protections under the First Amendment of the US constitution.

In other leaks, the Guardian reported that the CIA had asked US diplomats to gather information on Secretary-General Ban Ki-moon and other senior UN figures. The United States came under fire after WikiLeaks documents released on Sunday showed that Secretary of State Hillary Clinton had asked American diplomats at the UN to seek intelligence about Ban. The July 31, 2009 cable requested information about the UN leader's stance on Iran and the Middle East and his "management and decision-making style."