IRNA - Iranian Deputy Foreign Minister Abbas Araghchi in a message elaborated on the reason behind arresting UK ambassador to Tehran Rob Macaire, saying he was busted as a foreigner in an illegal gathering.

"He wasn't detained, but arrested as an unknown foreigner in an illegal gathering," Araghchi tweeted on Sunday in response to High Representative of the European Union Josep Borrell who had said: "Very concerned about the temporary detention of the UK Ambassador @HMATehran in Iran."

"Full respect of the Vienna convention is a must. The EU calls for de-escalation and space for diplomacy," Borrell noted.

"When police informed me a man was arrested who claims to be UK Amb, I said IMPOSSIBLE! only after my phone conversation w him I identified, out of big surprise, that it's him. 15 min later he was free."

The UK Foreign and Commonwealth Office has commented on the detention of its ambassador in Tehran, terming it as being against international norms.

Some parliamentarians urged the Ministry of Foreign Affairs to take the necessary measures against the UK ambassador's move, which they said is "against all international norms".

Iranian Foreign Ministry said earlier on Sunday that it is waiting for the police report on detention of the UK Ambassador to Tehran Rob Macaire.