WikiLeaks, the online portal set up to disseminate secret documents, is set to publish the largest single horde of documents, some 400,000 military reports in Iraq.
In a global operation the material will be sent to The New York Times, The Guardian and Der Spiegel within the next week, possibly as early as tomorrow.
Security officials in Britain and America are urging against the release, arguing that that publication could endanger national security.
Julian Assange, the websites founder, is justifying the release on the grounds that it documents the history of the war.
The volume of classified information dwarfs a previous leak in July which covered the Afghanistan war. That release was widely condemned for revealing the names and identities of Afghan informants.