The Korean Central News Agency made the announced that Kim was awarded the title of marshal Wednesday, which makes him the supreme commander of the country's military.
The announcement follows shake-ups in Kim's inner circle of advisers. Ri Yong Ho was removed from his post as army chief Sunday for what the government said was "illness." Gen. Hyon Yong Chol was promoted to the rank of vice marshal following Ri's ouster this week.
Patrick Ventrell, a spokesman for the U.S. State Department, said that unless Pyongyang makes significant reforms, "changes in personnel ... mean little."
Washington had promised to deliver substantial food assistance to North Korea after the regime placed a moratorium on long-range missile and nuclear tests early this year. The deal collapsed, however, after North Korea tried to send a long-range rocket into orbit in April.
Missile launches in 2006 and 2008 by North Korea coincided with nuclear tests.
The shuffling comes eight months after the December death of North Korea leader Kim Jong Il. Kim Jong Un, his son, has since taken control over the country.