Iran's leaders have faced a second day of protests following their admission the military shot down a Ukrainian passenger plane, killing all 176 people on board, many of them Iranians.
Protesters in Tehran and in several other cities chanted slogans against the leadership.
Clashes with security forces and the firing of tear gas are reported.
Iran admitted "unintentionally" hitting the plane after initially denying it, amid rising tensions with the US.
The plane, en route to the Ukrainian capital, Kyiv, was shot down near Tehran last Wednesday, shortly after Iran had launched missiles at two airbases housing US forces in Iraq.
Those strikes were a response to the US killing of senior Iranian commander Qasem Soleimani in a drone strike in Baghdad on 3 January.
Dozens of Iranians and Canadians, as well as nationals from Ukraine, the UK, Afghanistan and Sweden died on the plane.
What happened at Sunday's protests?
Demonstrators attended new protests despite a large deployment of security forces.
Riot police, members of the elite Revolutionary Guard on motorbikes, and plainclothes security officials were out in force.
In one apparently symbolic act rejecting state propaganda, video showed students taking care not to walk over US and Israeli flags painted on the ground at Shahid Beheshti university in Tehran.
In some social media clips, protesters can be heard chanting anti-government slogans, including: "They are lying that our enemy is America, our enemy is right here." Many of the protesters are women.
Social media footage showed clapping and chanting protesters in Tehran's Azadi Square. BBC Persian says there has been a crackdown there by security forces, with tear gas fired.
The semi-official Fars news agency said up to 1,000 people were protesting at various points in the capital.
Protests were also reported in other cities.
Those who decide to continue demonstrating will be mindful of the violence with which the security forces have dealt with protest movements in the past, the BBC's Arab affairs editor Sebastian Usher says.
On Saturday, students had gathered outside two universities. They initially did so to pay respect to the victims, but angry protests erupted later in the evening and tear gas was reportedly fired to disperse them.
A number of Iranian newspapers have covered the vigils for the plane victims alongside headlines such as "Shame" and "Unforgivable".
But there has also been praise for what one pro-government newspaper called Iran's "honest" admission of error.
There were also protests on Sunday in Tehran in support of Soleimani, and opposing the US and UK.
What has the international reaction been?
US President Donald Trump on Sunday repeated warnings that Iran should not target anti-government protesters, saying, "the World is watching. More importantly, the USA is watching".
To the leaders of Iran - DO NOT KILL YOUR PROTESTERS. Thousands have already been killed or imprisoned by you, and the World is watching. More importantly, the USA is watching. Turn your internet back on and let reporters roam free! Stop the killing of your great Iranian people!— Donald J. Trump (@realDonaldTrump) January 12, 2020
Britain, meanwhile, has condemned the arrest of the UK ambassador to Iran in Tehran as a "flagrant violation of international law".
Foreign Secretary Dominic Raab said Rob Macaire was detained after attending a vigil where he was paying respects to victims of the crash, some of whom were British.
Mr Macaire said he left the vigil when some people started chanting and had played no part in the demonstration.
Iran on Sunday summoned the ambassador to complain about "his unconventional behaviour of attending an illegal rally", the foreign ministry website said.
Iranian protesters set a UK flag alight in front of the UK embassy on Sunday.
In other developments on Sunday:
- US Defence Secretary Mark Esper told CBS's Face the Nation on Sunday that he "didn't see" specific evidence that Iran was preparing attacks against US embassies. President Trump had said on Friday he believed four embassies were under threat. Mr Esper said he shared the president's belief that there "probably and could've been attacks on additional embassies"
- Eight Katyusha rockets were fired at the Balad air base, which has housed US forces north of the Iraqi capital, Baghdad. Four Iraqis were wounded. There have been several recent attacks on the base blamed on Iranian-backed militias
- Hundreds of mourners are attending memorials in the Canadian cities of Toronto and Edmonton, At the latter, Prime Minister Justin Trudeau told the crowd he would pursue justice and accountability on behalf of their families and friends
At the scene: Canada mourns
BBC's Jessica Murphy, Edmonton, Alberta
Pedram Mousavi and Mojgan Daneshmand gazed out from the photograph projected on the screen with wide smiles, looking like they had been caught laughing at a shared joke.
The "sweet couple" likely were.
Along with their two daughters, Daria, 14, and Dorina, 9, they were remembered for their quickness to laughter, their generosity, their full embrace of life.
The family of four were among the 13 victims of flight PS752 who came from the Canadian city of Edmonton.
A crowd of some 2,300 people packed into a university gym on Sunday to pay respects to those lost - family, close friends colleagues, classmates - whose death has left a hole in so many lives.
Canadian Prime Minister Justin Trudeau told the crowd that in their sorrow "your entire country stands with you".
A friend of Pedram's, through a letter read by his former student Hossein Saghlatoon, said the loss was "too much to bear".
He was looking forward to many more memorable moments with Pedram and his family, he wrote "but alas, the cruel hand of destiny had some other plans".
How did the Iranian admission unfold?
For three days, Iran denied reports its missiles had brought down the plane, with one spokesman accusing Western nations of "lying and engaging in psychological warfare".
But on Saturday morning, a statement read on state TV accepted the plane had been shot down.
Brig-Gen Amir Ali Hajizadeh, the Revolutionary Guards' aerospace commander, said a missile operator had acted independently and alone, mistaking the plane for a "cruise missile".
He also said he had informed the authorities about what had happened on Wednesday, raising questions about why Iran had denied involvement for so long.
Both Ukrainian President Volodomyr Zelensky and Justin Trudeau have demanded accountability from Iran.
Mr Trudeau said on Saturday there must be a full investigation with "full clarity on how such a horrific tragedy could have occurred".