Under the Islamic republic's constitution, the supreme leader is also commander-in-chief and appoints all armed forces chiefs, including the police.
Reports in all state media said that Brigadier General Mohammad Reza Naghdi, a veteran Basiji, had replaced cleric Hojjatoleslam Hossein Taeb as commander of the Basij (Mobilisation) force.
The Basij, comprising hundreds of thousands of volunteers, reputedly swung its weight behind Mahmoud Ahmadinejad in the 2005 election that won him the presidency over heavyweight former president Akbar Hashemi Rafsanjani.
The Basij is a unit of the Revolutionary Guards.
In the aftermath of the June 2009 election, Basij members were among the security forces mobilised to crack down on protesters disputing the outcome of the vote that returned Ahmadinejad to power.
Brigadier General Mohammad Hejazi was appointed deputy chief of Iran's armed forces, replacing Naghdi, media reported.
Brigadier General Hossein Salami, commander of the Guards' air force, was promoted to deputy commander of the Revolutionary Guards, the post previously held by Hejazi.
The new commander of the Guards' air wing was named as Brigadier General Amir Ali Hajizadeh.
The Revolutionary Guards is a fiercely committed ideological force whose influence extends beyond the military into politics and the economy.
No reasons were given for Sunday's top brass changes, and no additional information was supplied.
