The WikiLeaks founder, Julian Assange, today hailed the person responsible for leaking the diplomatic cables as "an unparalleled hero" and suggested that his organisation had deliberately used servers in certain jurisdictions, such as Amazon's in the US, to test their commitment to freedom of speech.

In a live Q&A on theguardian.com, the Australian journalist highlighted the role alleged to have been played in the leaks by the soldier Bradley Manning.

"For the past four years one of our goals has been to lionise the source who take the real risks in nearly every journalistic disclosure and without whose efforts, journalists would be nothing," said Assange. "If indeed it is the case, as alleged by the Pentagon, that the young soldier – Bradley Manning – is behind some of our recent disclosures, then he is without doubt an unparalleled hero."

Assange was answering questions online as it was claimed that he faced imminent arrest. AFP reported that the Swedish authorities had issued a new international arrest warrant containing information requested by British police.

During the live Q&A, Assange responded to Amazon.com's decision earlier this week to pull the plug on hosting WikiLeaks. On Wednesday, the company announced it was cutting off WikiLeaks after being contacted by the staff of Joe Lieberman, chairman of the Senate's committee on homeland security.

He said: "Since 2007 we have been deliberately placing some of our servers in jurisdictions that we suspected suffered a free speech deficit in order to separate rhetoric from reality. Amazon was one of these cases."

His comments on the matter came after WikiLeaks tweeted that if Amazon was "so uncomfortable with the first amendment, they should get out of the business of selling books."

Despite facing arrest warrants over allegations of sexual crimes in Sweden, Assange found time to answer a reader's question about extraterrestrial life.

Asked whether WikiLeaks had ever received documents relating to UFOs, he said: "Many weirdos email us about UFOs or how they discovered that they were the antichrist whilst talking with their ex-wife at a garden party over a pot-plant."

However, he said, none had yet satisfied the twin publishing criteria: "that the documents not be self-authored; that they be original."

But he added: "It is worth noting that in yet-to-be-published parts of the cablegate archive there are indeed references to UFOs."

Meanwhile, Assange's lawyer, Mark Stephens, told the Guardian that neither he nor his colleagues had heard from police about the arrest warrants.

"We had an understanding with Scotland Yard of long standing that in the event they wanted to contact Julian Assange they would come to us and we would facilitate a congenial and convenient meeting," he said.

"I hope the police remember their undertaking. I've had no indication that anyone wants to talk to Julian at this moment in time; no member of his legal team has had a call from any law enforcement agency."