In this photograph taken on January 11, Iranian police officers take position while protesters gather in front of Amir Kabir University in Tehran, to remember victims of a Ukrainian airplane shot down by an Iranian missile.
It was not immediately possible to authenticate the video.
All 176 people on the Ukraine-bound flight last Wednesday were killed. There were no survivors.
Video also showed dozens of police in riot gear in another area of Tehran. Even so, the leader of the Lebanese militant group Hezbollah, which is closely aligned with Iran, said Sunday that Iran's missile attacks on two bases in Iraq housing US forces last week were only the start of the retaliation.
"On Iran, they discussed the tragic loss of life on the Ukraine International Airlines passenger jet".
Videos posted late on Sunday recorded the gunfire around protests in Tehran's Azadi Square.
Protesters chanted "Death to dictator" and against the Revolutionary Guards, Fars news agency said, a rare move for a country where media usually refer to demonstrators as "rioters" and refrain from publishing such slogans.
At earlier protests on Saturday, students in Tehran shouted: "They are lying that our enemy is America!" The veracity of the footage and witness accounts could not be independently verified.
In a statement carried by Iran's state broadcaster's website on January 13, Tehran's police chief Hossein Rahimi denied that shots had been fired at protesters.
Iran's latest showdown with the U.S. has come at a precarious time for the authorities in Tehran and their allies across the Middle East, when sanctions imposed by Trump have caused deep harm to the Iranian economy.
The scenes recall the anti-government protests across Iran in November which saw at least 300 people killed and thousands arrested across the country, according to Amnesty International. "The Iranian government is at a cross-roads moment".
"The reality is that we did not lie", he added, blaming "a lack of valid information" and also "the US's psychological warfare" for his own and other officials' denials that the plane was shot down. "I can tell you that they are damaged", said Fox.
Trump also used Farsi to call on the Iranian government "not to kill protesters" and express that it's "totally up to" Iran to start negotiations, as he "couldn't care less" about it.
Trump precipitated an escalation with Iran in 2018 by pulling out of a deal under which sanctions were eased in return for Iran curbing its nuclear programme.
Iran has repeatedly said it will not negotiate as long as United States sanctions are in place. It denies seeking nuclear arms.
Iranian leaders promised to avenge the killing and launched airstrikes against Iraqi bases housing USA troops. Gen. Qassem Soleimani, in an airstrike in Baghdad earlier this month. "Stop the killing of your great Iranian people!" The Ukrainian plane, on its way to Kiev and carrying many Iranian dual nationals, crashed hours later.
Iran's government on Monday denied a "cover-up" after its armed forces took three days to admit that a passenger plane was downed by mistake last week.
President Hassan Rouhani promised a "thorough investigation" into the disaster in a phone call with Sweden's Prime Minister Stefan Lofven, his office said.
The plane took off despite heightened tensions after Iran's missile attack on Iraqi bases housing US troops earlier on the day of the tragedy.
Canadians held vigils for the victims.
Fox added that Canada's investigation will pose questions that will be "very uncomfortable" for Iran.
That same day, the U.K.'s ambassador to Iran, Rob Macaire, was briefly arrested near a demonstration in Tehran. Under the 1961 Vienna Convention on Diplomatic Relations, ambassadors have diplomatic immunity.