Videos posted on Twitter showed hundreds of people chanting Protesters demanded stepping down after Ukrainian plane incident TEHRAN: The British ambassador to Iran was arrested on Saturday amid protests demanding Supreme Leader Ayatollah Ali Khamenei step down after Tehran said its military had mistakenly shot down a Ukrainian plane, killing 176 people. Robert Macaire was present during demonstrations in front of Tehran’s Amir Kabir University and was arrested after allegedly "inciting" a crowd, Iran"s Tasnim news agency reported. The 53-year-old was released after several hours. Britain"s Foreign Secretary Dominic Raab said the arrest was without grounds or explanation and a "flagrant violation of international law." Videos posted on Twitter showed hundreds of people chanting “Commander-in-chief (Khamenei) resign, resign” in front of Tehran’s Amir Kabir university. In a message to the protesters, Donald Trump said the US was following the demonstrations closely and was "inspired by your courage." "To the brave, long-suffering people of Iran: I"ve stood with you since the beginning of my Presidency, and my Administration will continue to stand with you." he said on Twitter. Iran announced Saturday that its military “unintentionally” shot down the jetliner, after the government had repeatedly denied Western accusations that it was responsible. The plane was shot down early Wednesday, hours after Iran launched a ballistic missile attack on two military bases housing US troops in Iraq in retaliation for the killing of Iranian General Qassem Soleimani in an American airstrike in Baghdad. No one was wounded in the attack on the bases.