The anti-secrecy website WikiLeaks on Thursday accused a journalist with the Guardian of leaking the passwords to a trove of unredacted US diplomatic cables, charges denied by the British newspaper.

"A Guardian journalist has, in a previously undetected act of gross negligence or malice, and in violation of a signed security agreement with the Guardian's editor-in-chief Alan Rusbridger, disclosed top secret decryption passwords to the entire, unredacted, WikiLeaks Cablegate archive," it said.

"We have already spoken to the (US) State Department and commenced pre-litigation action. We will issue a formal statement in due course," WikiLeaks added, in a statement posted on Twitter.

The Guardian, one of a handful of newspapers that began publishing redacted cables last year, said WikiLeaks shared the documents through a secure server for a period of hours before taking the server offline and removing the files.

"But unknown to anyone at the Guardian, the same file with the same password was republished later on BitTorrent, a network typically used to distribute films and music," the newspaper reported.

The Guardian went on to deny, in an official statement, allegations that the password had been released through its book, "WikiLeaks: Inside Julian Assange's War on Secrecy," published in February. "It's nonsense to suggest the Guardian's WikiLeaks book has compromised security in any way," the Guardian said.

"Our book about WikiLeaks was published last February. It contained a password, but no details of the location of the files, and we were told it was a temporary password which would expire and be deleted in a matter of hours. It was a meaningless piece of information to anyone except the person(s) who created the database."

The Guardian instead reported that a link to the full, unredacted database was published by an unnamed Twitter user who found it after acting on hints published in several media outlets and on WikiLeaks's Twitter feed.

The security breach has led to the publication of the WikiLeaks archive of 251,000 diplomatic cables online, without redaction to protect sources who spoke to US diplomats on condition of anonymity, the Guardian said.

Redacted cables released over the past nine months through agreements with the major newspapers and by WikiLeaks itself have revealed confidential diplomatic assessments and potentially embarrassing comments by world leaders.

WikiLeaks has defended the release of the embassy cables -- as well as the previous release of leaked Iraq and Afghanistan war reports -- as the journalistic exposure of official deception.

The United States, while refusing to confirm the authenticity of any of the documents, has accused WikiLeaks of putting individual lives and US national security at risk.