Armed forces spokesman General Alireza Afshar took over the job of deputy interior minister for political affairs from Mojtaba Samareh Hashemi, one of the president's advisers.
Hashemi will remain in his other post as top adviser to the president.
Like Ahmadinejad, Afshar has a background in Iran's elite Revolutionary Guards.
Guardians Of Iran's Revolution?
The Islamic Revolutionary Guards Force (pasdaran) was created in 1979 by the father of the Iranian Revolution, Ayatollah Ruhollah Khomeini, to safeguard that revolution.
The IRGC has several components whose numbers are widely disputed, but any serious estimates put their ranks at upward of 100,000. They operate independently or in cooperation with regular army forces.
President Mahmud Ahmadinejad reportedly served during the Iran-Iraq War as an instructor for the IRGC's volunteer-based Basij, a blunt official instrument to police moral values. IRGC allies form an influential segment of Ahmadinejad's power base.
Many of the most recent accusations emerging from the United States have involved the so-called Quds (Jerusalem) Force, whose responsibilities include extraterritorial operations that initially included efforts to export Iran's Shi'ite revolution. The Quds Force officially reports directly to the country's supreme leader, currently Ayatollah Ali Khamenei.