U.S. officials tell The Associated Press that the Defense Department will take over background investigations for the federal government, using increased automation to tighten controls and tackle a massive backlog of workers waiting for security clearances.

The change aims to address gaps and delays in a system that were highlighted by the case of a Navy contractor who later gunned down a dozen people at Washington's Navy Yard in 2013.

Pentagon officials say that over the next three years, the department will take responsibility for all background investigations involving its military and civilian employees and contractors.

And according to a U.S. official, the White House is expected to soon give the Defense Department authority to conduct security reviews for nearly all other government agencies as well.