An EU delegation was stopped Sunday from speaking to foreign media in Tehran, with an Iranian security official threatening action against reporters and photographers if they tried to film the incident.
Having called a press conference at their hotel in the capital, the plans of the Foreign Affairs Committee of the European Parliament were disrupted, prompting an angry exchange on the street.
After being ushered off hotel premises, Elmar Brok, chairman of the committee, angrily told the security official: "You cannot stop me from talking to reporters."
But Brok, a German MEP, was pointedly warned he had no right to speak to media near the end of a two-day trip, which comes as world powers near a June 30 deadline for a deal on Iran's disputed nuclear programme.
A crew from Press TV, Iran's English language channel which is broadcast worldwide, was invited to interview Brok but he cancelled the engagement.
Foreign journalists were earlier told by a hotel manager that there was no permission for a press conference.
Photographers and video reporters were also warned by the security official that they would face repercussions if they used their equipment in any way.
The activities of foreign media in Iran, particularly Western outlets, are strictly controlled and subject to multiple regulations and restrictions by authorities.
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Sunday's incident occurred despite the group of seven EU lawmakers being invited to Tehran by their Iranian counterparts.
"This is an old behaviour which has nothing to do with the new politics of Iran," Brok later told AFP by telephone, alluding to hopes of better political relations if there is a nuclear deal.
"It leaves a bad impression but this unhappy incident did not spoil the visit," he added.
The group, which will leave Tehran later Sunday, was the first European parliament delegation to visit Iran since December 2013.
On April 2, Iran and the P5+1 -- the United States, Britain, China, France, Russia plus Germany -- agreed the main outlines of the nuclear deal, with Tehran agreeing to mothball parts of its atomic programme.
The EU delegation met senior Iranian politicians including parliament speaker Ali Larijani and Masoumeh Ebtekar, one of Iran's vice presidents.
"With this visit the European Parliament wants to give a strong signal of its commitment to building trust in this key moment in EU-Iran relations," Brok said separately in a statement.
The talks centred on instability in the Middle East, including in Syria, Iraq and Yemen, as well as drug smuggling in neighbouring Afghanistan, climate change and the environment.
Human rights, a regular area of contention between Iran and the West, were also discussed.