WikiLeaks founder Julian Assange phoned the White House to warn lives would be put at risk by the publication of cables online, a court has heard.

On 25 August, 2011, German news outlet Der Freitag revealed that it was possible to access the unredacted database of cables by using a mirror site and a 58-key password that had been published in a book by The Guardian earlier in the year.

In a phone call to the White House on the same day, WikiLeaks had asked to speak to then secretary of state Hillary Clinton as “a matter of urgency” over fears the information was about to be dumped online.

Mr Assange had warned: “I don’t understand why you’re not seeing the urgency of this. Unless we do something, then people’s lives are put at risk.”

According to Mark Summers QC, representing Assange, the State Department had responded by suggesting that Assange call back “in a couple of hours”.

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Mr Assange is currently fighting extradition from the UK to the US to face trial on 18 charges over the leaking of hundreds of thousands of classified documents in 2010 and 2011. He is accused of conspiring to steal from and hack into US department of defence computers, along with former US army intelligence analyst Chelsea Manning.

Prosecutors claim he knowingly put hundreds of intelligence sources around the world at risk of torture and death by publishing unredacted documents containing names or other identifying details.

But Mr Summers argued on Tuesday that the extradition request “boldly and brazenly” misrepresents the facts.

Mr Summers said WikiLeaks had begun redacting a tranche of 250,000 leaked cables in November 2010, working with media partners around the world.

“That process involved the US government and state department feeding suggested redactions to the media,” he said. “Knowing the US government was involved in the redaction process, can it be in any way said the request represents a fair or accurate representation of what occurred?”

Mr Summers blamed the publication of the unredacted database of documents on the 2011 Guardian book about WikiLeaks.

He said: “Far from being a reckless, unredacted release, the world knows, every reporter in this room knows, the US government knows, that what actually occurred was that one of the media partners published a book in February 2011 and published the password to the unredacted materials, which then enabled the entire world to publish those unredacted materials in a book and they circulated on the internet, not on the WikiLeaks site, but on other sites.

“None of them have been prosecuted, some of which are US-based, all of them published first, some of them are still there.”

Responding to the claims made in court, a Guardian spokesperson said: “It is entirely wrong to say the Guardian’s 2011 WikiLeaks book led to the publication of unredacted US government files.

“The book contained a password which the authors had been told by Julian Assange was temporary and would expire and be deleted in a matter of hours. The book also contained no details about the whereabouts of the files. No concerns were expressed by Assange or WikiLeaks about security being compromised when the book was published in February 2011. WikiLeaks published the unredacted files in September 2011.”

Mr Assange is also accused of encouraging Ms Manning to steal classified documents, which allegedly included a bid to crack a password “hash” (a scrambled password) on US department of defence computers to anonymously access a classified network called the Secret Internet Protocol Network. But his lawyers point to evidence given by Ms Manning at her own 2013 court martial, which they say refutes these claims.

James Lewis QC, representing the US government, said in court: “Mr Assange didn’t have to publish the unredacted cables, he decided to do so. And he decided to do so on a widely followed and easily searchable website, knowing that it was dangerous to do so. That is the allegation and that is the offence.”