The anti-secrecy website WikiLeaks has confirmed reports of a security breach that has led to a massive amount of U.S. diplomatic cables being released onto the Internet with the names of sources revealed.

In a statement posted Thursday, WikiLeaks blamed Britain's Guardian newspaper for the disclosure, saying that a journalist revealed the password to unlock the entire unredacted archive in a book on WikiLeaks published earlier this year.

A spokesman for the newspaper denied any wrongdoing, saying they were told that the password would expire within hours. It adds that no details on the location of the files was published.

Until now, WikiLeaks had released censored versions of U.S. diplomatic cables, as well as confidential material on the wars in Iraq and Afghanistan.

The breach has led to the publications of some 251,000 cables online, which contain sensitive information that could put U.S. sources at risk.

The U.S. State Department says WikiLeaks informed it of their impending release of the documents, but ignored appeals not to make them public.

State Department spokeswoman Victoria Nuland condemned Wikileaks' actions as “irresponsible, reckless and dangerous,” adding that the department is not working with the group. She added that the release threatens U.S. national security and the safety of confidential informants.