WikiLeaks, battling to remain online after sparking an international furor with its release of secret US cables, accused Amazon on Friday of cowardice for booting the website off its servers.
The Seattle-based Amazon, meanwhile, broke days of silence and provided its first public explanation of its decision to withdraw its Web-hosting services from WikiLeaks.org.
Amazon Web Services, in a statement, said it cut off WikiLeaks because it had violated the company's terms of service and not because of any government pressure.
WikiLeaks fired back with a message on its Twitter feed. "Amazon's press release does not accord with the facts on public record. It is one thing to be cowardly. Another to lie about it," it said.
WikiLeaks founder Julian Assange said WikiLeaks had deliberately chosen to place servers "in jurisdictions that we suspected suffered a free speech deficit in order to separate rhetoric from reality."
"Amazon was one of these cases," Assange said in a question and answer session with readers on The Guardian newspaper's website.
Amazon is best known as an online retailer but it is also a major provider of Web-hosting services, renting out space on its computer servers to customers around the world.
In its statement, Amazon said "there have been reports that a government inquiry prompted us not to serve WikiLeaks any longer. That is inaccurate."
"There have also been reports that it was prompted by massive DDoS attacks," the company said in a reference to distributed denial of service attacks on the WikiLeaks website.
"That too is inaccurate," Amazon said. "There were indeed large-scale DDoS attacks, but they were successfully defended against."
DDoS attacks occur when legions of zombie computers, machines infected with viruses, are commanded to simultaneously visit a website, slowing it down or crashing it completely.
EveryDNS.net, the US domain name system service that had been sending traffic to WikiLeaks.org, pulled the plug on the website late on Thursday, saying the cyberattacks were threatening its 500,000 other clients.
Another US company, Tableau Software, cut off WikiLeaks on Wednesday citing a violation of its terms of service. Tableau Software was being used by WikiLeaks to create charts of its cache of secret US diplomatic cables.
Tableau Software said the move was in response to a call from US Senator Joe Lieberman, who said "no responsible company -- whether American or foreign -- should assist WikiLeaks in its efforts to disseminate these stolen materials."
Amazon Web Services said it does not pre-screen its customers "but it does have terms of service that must be followed.
"WikiLeaks was not following them," it said.
Amazon's terms state that customers must "control all of the rights to the content" stored on its servers and that the content "will not cause injury to any person or entity."
"It's clear that WikiLeaks doesn't own or otherwise control all the rights to this classified content," Amazon said.
"Further, it is not credible that the extraordinary volume of 250,000 classified documents that WikiLeaks is publishing could have been carefully redacted in such a way as to ensure that they weren't putting innocent people in jeopardy," the company said.
Some of the data stored by customers on Amazon's servers is controversial "and that's perfectly fine," the company said.
"But when companies or people go about securing and storing large quantities of data that isn't rightfully theirs, and publishing this data without ensuring it won't injure others, it's a violation of our terms of service, and folks need to go operate elsewhere," Amazon said.
WikiLeaks was offline for several hours after EveryDNS.net withdrew its services but reappeared on Friday with a Swiss domain name, WikiLeaks.ch.
WikiLeaks.ch only remained online for a few hours, however, forcing WikiLeaks to launch new addresses in the Netherlands, Germany and Finland: wikileaks.nl, wilileaks.de and wikileaks.fi.