LONDON — WikiLeaks -- whose spectacular publication of classified data shook world capitals and exposed the inner workings of international diplomacy -- may be weeks away from collapse, the organization's leader said.

Although its attention-grabbing leaks spread outrage and embarrassment across military and diplomatic circles, WikiLeaks' inability to overturn the block on donations imposed by American financial companies may prove its undoing.

"If WikiLeaks does not find a way to remove this blockade we will simply not be able to continue by the turn of the new year," founder Julian Assange told journalists Monday at London's Frontline Club. "If we don't knock down the blockade we simply will not be able to continue."

As an emergency measure, Assange said his group would cease what he called "publication operations" to focus its energy on fundraising. He added that WikiLeaks -- which he said had about 20 employees -- needs an additional $3.5 million to keep it going into 2013.

WikiLeaks, launched as an online repository for confidential information, shot to notoriety with the April 2010 disclosure of footage of two Reuters journalists killed by a U.S. military strike in Baghdad.

The Pentagon had claimed that the journalists were likely "intermixed among the insurgents," but the helicopter footage, which captured U.S. airmen firing on prone figures and joking about "dead bastards," unsettled many across the world.

The video was just a foretaste. In the following months, WikiLeaks published nearly half a million secret military documents from the wars in Iraq and Afghanistan. As a whole the documents provided an unprecedented level of detail into the grueling, bloody conflicts. Individually, many raised concerns about the actions of the U.S. and its local allies -- for example by detailing evidence of abuse, torture and worse by Iraqi security forces.

Although U.S. officials railed against the disclosures, claiming that they were putting lives at risk, it wasn't until WikiLeaks began publishing a massive trove of 250,000 U.S. State Department cables late last year that the financial screws began to tighten.

One after the other, MasterCard Inc., Visa Europe Ltd., Bank of America Corp. Western Union Co. and Ebay Inc.'s PayPal stopped processing donations to WikiLeaks, starving the organization of cash as it was coming under intense political, financial and legal pressure.

Assange said Monday that the restrictions -- imposed in early December -- had cut off some 95 per cent of the money he believes his organization could have received.

WikiLeaks spokesman Kristinn Hrafnsson defended the estimate as "conservative," noting that in 2010 the average monthly donation to WikiLeaks had been more than 100,000 euros ($140,000), while in 2011 the amount had fallen to between 6,000 and 7,000 euros.

Each company has given its own explanation for the blockade, expressing some level of concern over the nature of the secret-spilling site. But WikiLeaks supporters often point out that MasterCard and Visa still process payments for fringe groups such as the American Ku Klux Klan or the far-right British National Party and that neither WikiLeaks nor any of its staff have been charged with any crime.

Assange said his group was being subjected to corporate censorship, a sentiment backed by Dave Winer, a visiting scholar at New York University's Arthur L. Carter Journalism Institute.

"This was done without due process, without any charges, and has been in place since December last year," he said in a blog post about the blockade. "If I want to give $100 to WikiLeaks, and if I want to use my credit card to do so, who are they to say I can't?"

WikiLeaks has recently taken steps to work around the blockade, including a series of auctions and moves toward cellphone-enabled donations. Assange said Monday that his group was switching its focus from soliciting small-time donations, which typically net about $25, to getting money from a "constellation of wealthy individuals."

He didn't elaborate, but Assange has several wealthy backers, including Frontline Club founder Vaughan Smith, whose manor house in eastern England has been put at Assange's disposal while he fights extradition to Sweden on sex crime allegations.

A decision on whether to extradite him is expected in the next few weeks. Speaking to journalists after Monday's appearance, Assange put his chances of being extradited without the possibility of appeal at "30 per cent."

Also looming in the background is a U.S. grand jury investigation into WikiLeaks' disclosures. Earlier this month, a small California-based Internet provider became the second company to confirm it was fighting a court order demanding customer account information as part of the American WikiLeaks inquiry.

WikiLeaks' suspected source, U.S. Army intelligence analyst Bradley Manning, remains in custody at Fort Leavenworth prison in Kansas.