The Foreign and Commonwealth Office of Britain on Monday summoned the Iranian ambassador to explain why the British envoy in Tehran was detained by the police in violation of international conventions.

Hamid Baeidinejad was summoned after Rob Macaire was held by police on Saturday after attending a vigil for the victims of the Ukrainian plane shot down last week by the Revolutionary Guard, killing all 176 passengers and crew members.

Yesterday in a tweet Macaire said he wasn't taking part in any demonstrations. " Went to an event advertised as a vigil for victims of #PS752 tragedy. Normal to want to pay respects — some of victims were British. I left after 5 mins, when some chanting started," he wrote and added that he was detained half an hour after leaving the area.

"Arresting diplomats is of course illegal, in all countries," the British ambassador said in his tweet.

Foreign Secretary Dominic Rabb condemned the UK ambassador's arrest in Tehran "without grounds or explanation" and described it as a flagrant violation of international law.

Tasnim News Agency affiliated with Revolutionary Guard claimed that the British ambassador who was arrested for "instigating and organizing suspicious activities in front of Amir Kabir University" where a large protest rally was underway. Tasnim also claimed that a "shop opposite Amir Kabir University was the main place" for the British ambassador's purported activities.