The family of a prominent Iranian poet, Mohammad Mokhtari, say he's been missing since Thursday and they're extremely concerned for his safety.

Mr Mokhtari and a group of other Iranian writers have been repeatedly questioned by a revolutionary court for trying to reactivate a professional association of Iranian writers.

Last week, another dissident writer Majid Sharif died in suspicious circumstances after disappearing for four days, and concern has also been expressed over the disappearance of an activist Piruz Davani who disappeared more than two months ago.

Two opposition leaders, Dariush Foruar and his wife Parvaneh, were stabbed to death at their Tehran home two weeks ago.

The Iranian opposition linked the disappearances to elements in the establishment who they say are trying to suppress increasingly open challenges to the government.