Reports say Iranian security personnel stopped a delegation from the European Parliament from speaking to foreign media in Tehran on June 7.
The delegation, headed by Germany's Elmar Brok, had planned a press conference at their hotel at the end of a two-day visit.
However, security officials at the hotel reportedly didn’t allow the press conference to take place, saying it had not been agreed with the hotel in advance.
Brok was also prevented from speaking to reporters outside the hotel and reporters were forced to leave.
Brok cancelled a planned interview with state-owned Press TV in protest.
Brok was quoted by the AFP news agency as saying: "It leaves a bad impression but this unhappy incident did not spoil the visit," he added.
The delegation met senior Iranian politicians including parliament speaker Ali Larijani and Masoumeh Ebtekar, one of Iran's vice presidents.