The Australian Federal Police initially classified its investigation into a high-profile national security leak as "routine" and of "low value", according to a cache of documents that also reveals police were armed when they launched two recent raids on the media.

Emails obtained by The Sydney Morning Herald and The Age under freedom of information laws also offer fresh evidence that Annika Smethurst, a senior member of the Canberra press gallery, could be prosecuted for publishing secret government information.

The AFP is expected to be called before a parliamentary inquiry to explain the chain of events leading to raids in early June on Smethurst's Canberra home and the Sydney headquarters of the ABC over separate stories based on sensitive and secret government information.

The search warrants sparked a major debate over press freedom, with media chiefs lobbying the Morrison government over recent days for swift legal changes to better protect whistleblowers and journalists.