An Iranian news agency says authorities detained the grandson of influential former president Akbar Hashemi Rafsanjani.
The semi-official Fars news agency says Hasan Lahouti was arrested in Tehran airport upon arrival from London late Sunday.
Today's report did not elaborate on why Mr Lahouti was detained.
Mr Rafsanjani, a powerful figure in Iran's clerical establishment, supported opposition leader Mir Hossein Mousavi in his challenge to President Mahmoud Ahmadinejad, who the opposition says won June elections by fraud.
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Iranian government has arrested thousands and put more than 100 on trial in a crackdown on the opposition since the election.
AP