Araghchi's remarks came in a tweet on Monday and in a reaction to a tweet of EU Foreign Policy Chief Josep Borrell.
"He was not detained but had been arrested as an unknown foreigner who was participating in an illegal gathering in Tehran," Araghchi wrote.
"When the Police informed me that an arrested man claims he is the UK ambassador to Iran, I said that is impossible," he added.
"After a phone conversation with him, I recognized him surprisingly," he said, "Some 15 minutes later he was released."
Borrell in a Sunday tweet wrote, “Very concerned about the temporary detention of the UK Ambassador @HMATehran in Iran. Full respect for the Vienna convention is a must. The EU calls for de-escalation and space for diplomacy.”
A group of students had gathered inside the university to voice their protest after Iran announced the unintentional downing of a Ukrainian plane.
The General Staff of the Iranian Armed Forces announced on Saturday that the country’s air defense unintentionally shot down a Ukrainian passenger plane on January 8 amid the highest level of readiness because of a possible military attack by the US.
According to IRNA, the Iranian Foreign Ministry has objected to the UK's envoy act and is waiting for the police report on the details.
The UK Foreign Ministry has also objected to the detention of its ambassador to Tehran and called it against international law.
The British ambassador has been reportedly summoned by Iranian ministry of foreign affairs.
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