Wikileaks is planning to release 400,000 more classified documents on the Iraq War, making it the single largest military leak in the US history.

The Pentagon set up a 120-person taskforce several weeks ago to go through the documents and determine their release impact.

The documents are expected to be released on Monday.

Colonel David Lapan, a Pentagon spokesman said the documents, obtained from an Iraq-based database, included "significant acts, unit-level reporting, tactical reports, things of that nature," AFP reported.

The documents contain "Significant activities" (SIGACTS), including information on attacks targeting coalition forces, Iraq's security forces, the civilian population and infrastructure, the US Defense Department announced.

Newseek earlier reported that some of the documents reveal US forces being involved in a "bloodbath." The Pentagon has asked the whistleblower website to return the classified documents to the US military.

It is expected that The New York Times, Britain's Guardian and Der Spiegel of Germany will be publishing the documents simultaneously.

In July, Wikileaks published 77,000 classified documents on the war in Afghanistan that were leaked by army soldier Bradley Manning.