The Pentagon searching for the source of leaked documents relating to the war in Afghanistan is focusing on Army Private Bradley Manning as the main suspect responsible for the leak of tens of thousands of documents.

Manning is thought to have accessed a worldwide military classified Internet and e-mail system to download these documents. The FBI is assisting the Defence Department in the investigation.

An unnamed Pentagon official said investigators believe Manning logged into a system called the Secret Internet Protocol Router Network which provides members of the military who have appropriate security clearances, access to classified e-mails and the military’s classified Internet system. Passwords and physical access are needed to log onto the system that provides information classified at the highest level.

Officials from the Pentagon said that the only information and material they have seen on a WikiLeaks.org this material classified as secret, which is a relatively low-level designation that allows access by a large number of military personnel.

Julian Assagne, the editor in chief of WikiLeaks.org has refused to say where his website obtained 90,000 US documents about the Afghan war. The majority of the documents were posted on the website last Sunday and has been called the biggest against leak since the Pentium papers about the Vietnam War.

Private Manning was first charged in June with eight violations of the US criminal code for allegedly transferring classified data including an earlier video that finished up on WikiLeaks.org. The private had top-secret clearance as an intelligence analyst for the Army when he was stationed in Iraq.