According to Iran’s Tasnim news agency, British ambassador in Iran, Rob Macaire was arrested as he tried to make his way back to the embassy. He was one of the people arrested outside the university on suspicion of organising, provoking and directing radical actions. It is unclear who he was arrested by.

UK Foreign secretary Dominic Raab said in a statement: "The arrest of our ambassador in Tehran without grounds or explanation is a flagrant violation of international law."

Raab added: "The Iranian government is at a crossroads moment. It can continue its march towards pariah status with all the political and economic isolation that entails, or take steps to de-escalate tensions and engage in a diplomatic path forwards."

Macaire was said to be "safe and well" in the British embassy after he was released after more than an hour in custody. 

His arrest came as a wave of anti-government demonstrations broke out across the country following the admission Iranian forces had accidentally brought down a Ukrainian airliner killing all 176 people on board.

It is understood that the ambassador had been attending what had been billed as a vigil for the victims of the crash at the Amir Kabir University.

The event however quickly turned into an anti-government protest at which point the ambassador was said to have left.