The head of Iran's judiciary says embattled President Mahmoud Ahmadinejad does not understand his constitutional powers.

It is the latest round in war of words between the two branches of government sparked by Ahmadinejad's attempt to visit a prison where an aide is being held.

Ahmadinejad once had the backing of the clerical establishment, but lost it when he was perceived to have challenged the country's Supreme Leader Ayatollah Ali Khamenei last year.

On Monday, Ahmadinejad accused the judiciary of "unconstitutional" behavior. He said he did not need permission to visit Evin prison near Tehran.

But judiciary chief Ayatollah Sadeq Larijani fired back that Ahmadinejad will not be allowed to visit Evin without his permission. His remarks were reported by the semi-official ISNA news agency Wednesday.