Journalists can be considered "unprivileged belligerents"

That's what the Department of Defense says in its "Law of War Manual". Thus, those reporting on the military in any capacity are open to be treated the same as spies - or even terrorists.

Some excerpts from the manual:

...journalists can be captured and held by the military for "engaging in hostilities," "spying" or "sabotage and similar acts behind enemy lines."

"Reporting on military operations can be very similar to collecting intelligence or even spying. A journalist who acts as a spy may be subject to security measures and punished if captured. To avoid being mistaken for spies, journalists should act openly and with the permission of relevant authorities." 

...journalists should "act openly and with the permission of relevant authorities."

Interestingly, most of the people the US military has imprisoned in Guantánamo, along with some held in Afghanistan, have been labeled "unprivileged belligerents."