"To the leaders of Iran - DO NOT KILL YOUR PROTESTERS. Thousands have already been killed or imprisoned by you, and the World is watching,” the US President wrote on the micro-blogging website Twitter.
"More importantly, the USA is watching. Turn your internet back on and let reporters roam free! Stop the killing of your great Iranian people!"
This comes hours after he viiced his administration’s support for the protesters saying that he has stood with them since he took office nearly three years ago.
Earlier on Saturday, British Ambassador to Iran Rob Macaire was temporarily arrested amid the ongoing anti-regime protests, the country's Tasnim news agency reported.
The agency said that Macaire was attempting "to organise, instigate and direct some radical and destructive action."
Thousands of people gathered in the Iranian capital on Saturday to stage protest after the regime admitted to having accidentally shot down a Boeing plane on 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.
Dozens of those who died in the plane crash were young Iranian students travelling to their studies in Canada.
Police dispersed the protesters with tear gas, according to reports and videos on social media. There were also reports of numerous arrests.