Protesters gathered in the Iranian capital Tehran on Saturday, in the wake of Iranian authorities admitting the military 'unintentionally' shot down a Ukrainian passenger plane on Wednesday.
The British ambassador to Iran has denied taking part in the protests, after he was briefly detained by authorities yesterday.
The UK has called the arrest of its ambassador a "flagrant violation of international law".
Iranian officials had initially denied being responsible for bringing down Ukrainian International Airlines flight PS752 on Wednesday, leading to the deaths of all 176 people on board.
However, amid increasing international pressure and growing evidence that an Iranian missile brought down the plane, Iran's military on Saturday acknowledged it was responsible - blaming 'human error'.
Reports from Tehran said demonstrations were held at two universities on Saturday, with demonstrators angry over the downing of the plane and officials' handling of the situation.
Images and videos shared online appeared to show tear gas being used as protesters clashed with police.
BBC reports that chants included "commander-in-chief resign" - referring to Iran's Supreme Leader Ali Khamenei - and "death to liars".
There were also reports of demonstrations in cities such as Shiraz, Isfahan, Hamedan and Orumiyeh.
The anti-government protests come only days after people took to the streets of the country in opposition to the US killing of top general Qasem Soleimani.
'The world is watching'
Amid the latest protest, US President Donald Trump overnight tweeted messages of support to the demonstrators in Iran.
In tweets shared in both English and Farsi, he wrote: "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.
"We are following your protests closely, and are inspired by your courage."
In a somewhat rare development, the semi-official Fars news agency featured a report on the anti-government demonstrations in the capital - saying the demonstrations chanted slogans against senior Iranian figures.
Meanwhile, Iran's moderate Etemad daily wrote in a banner headline on Sunday "apologise and resign" - claiming that the "people's demand" was that all those responsible for mishandling the plane crisis should quit.
Meanwhile, the British ambassador to Iran has denied taking part in yesterday's protests following his arrest yesterday.
Rob Macaire was detained for half an hour in Tehran before being released.
In a tweet, he confirmed he "wasn’t taking part in any demonstrations".
In a tweet on Sunday, he said: "[I] 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 started chanting."
He added that arresting diplomats is "of course illegal, in all countries".
Fars reported that an Iranian official told local media that Mr Macaire was arrested for "organising and provoking people to turn a mourning vigil [...] into an anti-government protest".
