In Iraq and Lebanon, governments backed by pro-Iran armed groups have also faced mass protests.
Tehran's police chief, however, said officers had been ordered to show "restraint" after Sunday night's gathering at iconic Azadi Square south of the city centre. The majority of those who died were Iranians.
General Salami, the current commander of the IRGC, officially apologized to the people of Iran and said that the government had not been informed that the plane was shot down until Friday evening.
The Kiev-bound airliner was knocked out of the sky hours after Tehran had launched a wave of missiles at Iraqi bases where USA troops are stationed in retaliation for the killing of top Iranian general, Qassem Soleimani, in Baghdad.
And if something happened to the protesters?
Footage circulating on social media showed protesters shouting "Death to the dictator", aimed at Supreme Leader Ayatollah Ali Khamenei and the system of clerical rule. Videos posted online showed demonstrators running from police who used batons and teargas. What appears to be gunfire can be heard.
"Oh my God, she's bleeding nonstop!" one person shouts in a video that shows a woman being carried away by a crowd that says she was shot in the leg. A pool of blood is seen on the ground.
Authorities denied that police had opened fire, while US President Donald Trump tweeted: "don't kill your protesters".
"We're willing to sit down and discuss without precondition a new way forward, a series of steps by which Iran becomes a more normal country, ' Defense Secretary Mark Esper said on CBS's 'Face the Nation".
Iran has repeatedly said it will not negotiate as long as United States sanctions are in place.
Taraneh Alidoosti, one of Iran's most famous actresses, posted a picture of a black square on Instagram with the caption: "We are not citizens".
Iran's president called the downing of the plane a "disastrous mistake".
What's the latest on the Flight PS752?
Protests videos and reports of the Iranian regime firing at the protesters were also reported by MEK Iran, an Albania-based organization that works for an Iran free from "oppression and Dictatorship".
"Some officials were even accused of lying and a cover-up but, in all honesty, that was not the case", he said.
A senior officer of Iran's Revolutionary Guard Corp., speaking on state television on Saturday, said an air-defence operator had mistaken the Ukrainian passenger jet for a cruise missile.
But a top Revolutionary Guards commander added to public fury when he said he told the authorities on the same day as the crash that an Iranian missile had struck the plane.
"He had 10 seconds to decide", he added.
House Speaker Nancy Pelosi said the congressional leadership should have been informed of the strike against Soleimani in advance.
Demonstrations over the "unforgivable mistake" started over the weekend.
Britain said its ambassador in Iran was briefly detained on Saturday, which Iranian media said was because he was inciting protests.
The TSB's director of investigations, Natacha Van Themsche, said Canadian investigators will meet Iranian officials on Tuesday, and that Iran has said it will allow the TSB to examine the wreckage of the airliner.
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