US State Department spokeswoman Morgan Ortagus tweeted calling on the Iranian regime to apologize for the detention of British Ambassador Robert Mackair.

"The Iranian regime arrested the British ambassador to Iran. This violates the Vienna Convention, which the regime has a notorious history of violating. We call on the regime to formally apologize to the UK for violating his rights and to respect the rights of all diplomats," she said.

A protest has been held in front of the building of Amirkabir University of Technology in Tehran. The UK Ambassador to Iran,  who was present at the protest, was detained for several hours on suspicion of involvement in provoking some radical actions among the protesters.

He was released a few hours later, but will come later to give an explanation in connection with the incident.

The rally was held in protest of the Ukrainian plane crash near Tehran. A group of students gathered to express their protest amid the crash.

As reported earlier, Ukrainian plane crashed near Tehran Airport on December 8, leaving all 176 people on board killed. Iranian Air Force General Staff admitted that a Ukrainian passenger plane was shot down near Tehran because of a human error. Iranian President Hassan Rouhani expressed deep regret over the tragedy and promised to bring those responsible to justice. The space forces of the IRGC claimed the full responsibility for the incident.