The U.S. Air Force is blocking its personnel from using work computers to view the websites of the New York Times and other major publications that have posted classified diplomatic cables, people familiar with the matter said.

Air Force users who try to view the websites of the New York Times, Britain's Guardian, Spain's El Pais, France's Le Monde or German magazine Der Spiegel instead get a page that says, "ACCESS DENIED. Internet Usage is Logged & Monitored," according to a screen shot reviewed by The Wall Street Journal....