WikiLeaks has been forced to suspend publishing classified files after a funding blockade and could have no option but to shut down by the end of the year, says founder Julian Assange.
The whistleblowing website has seen its funding plunge by 95 per cent due to an "arbitrary and unlawful financial blockade" mounted by companies including Visa and MasterCard since December last year, Assange said in London.
"In order to ensure our future survival, WikiLeaks is now forced to temporarily suspend its publishing operations and aggressively fundraise in order to fight back against this blockade and its proponents," he said.
"If WikiLeaks does not find a way to remove this blockade, given our current levels of expenditure we will simply not be able to continue by the turn of the New Year."
The Australian condemned the blockade as politically motivated and directly linked to "Cablegate", coming within days of the website's release of tens of thousands of classified US diplomatic cables in November last year.
Many relate to the wars in Iraq and Afghanistan while others contain frank and sometimes embarrassing assessments of world leaders made by US diplomats.
Assange said WikiLeaks was taking legal action against the blockade in several states including Britain, United States and Australia and has 100,000 publications pending, but warned it was facing an "existential threat".
The former computer hacker said WikiLeaks needed $3.5 million (2.5 million euros) to get through the next 12 months.
WikiLeaks spokesman Kristinn Hrafnsson explained that before the funding squeeze, average monthly donations exceeded 100,000 euros, but since then they had plunged to between 6,000 and 7,000 euros.
Assange claimed the blockade was part of "a concerted US-based, political attack that included vitriol by senior right-wing politicians, including assassination calls against WikiLeaks staff."
He said it had cost the organisation "tens of millions of dollars" in lost donations.
The former hacker also revealed that WikiLeaks had material on Bank of America, which it had previously threatened to release, but he admitted it was now in the custody of an employee that WikiLeaks suspended last August.
Despite 11 months of legal action and hopes of retrieving it, "at this stage we do not believe, unfortunately, that we will regain that material, which is a great loss," Assange said.
Returning to the funding issue, he said WikiLeaks has lodged an anti-trust complaint at the European Commission and expects a decision by mid-November on whether the European Commission Authority will open a full investigation.
He added: "A handful of US finance companies cannot be allowed to decide how the whole world votes with its pocket."
Assange announced that WikiLeaks would implement a new secure submission system for whistleblowers to send in confidential documents, to be launched on November 28 - the first anniversary of the so-called Cablegate release.
The new generation submission system will be safer than current online systems, which Assange claimed had been infiltrated by intelligence agencies.
The Australian said WikiLeaks has around 20 staff, about 800 volunteers and two million supporters. The average individual donation is $25.
Assange, 40, is currently living under strict bail conditions in Britain while he fights extradition to Sweden, where he is wanted for questioning over allegations of rape.
He denies the claims against him, saying they are politically motivated.