Iranian journalist Abdolreza Tajik has been prevented from flying to Spain to attend a seminar on the 30th anniversary of Iran's Islamic Revolution.
Several other Iranian intellectuals, including Iranian Nobel Peace Prize winner Shirin Ebadi, are attending the seminar.
Tajik told RFE/RL's Radio Farda that it is not clear why officials prevented him from leaving Tehran to give a speech at the seminar.
He said officials took away his passport without any explanation.
Tajik was one of the editors of the banned reformist daily "Shargh."
In recent years there have been several cases in which journalists or activists have been prevented from leaving Iran to attend international events.