"They are lying that our enemy is America, our enemy is right here," a group of protesters outside a university in Tehran chanted, according to video clips posted on Twitter.
Posts showed other demonstrators outside a second university and a group of protesters marching to Tehran's Azadi (Freedom) Square. The videos also showed protests in other cities.
Some state-affiliated media carried reports of the university protests, after Saturday's demonstrations sparked by Iran's announcement that its military had mistakenly brought down the Ukrainian plane on Wednesday, killing all 176 aboard.
Tehran residents told Reuters police were out in force in the capital on Sunday. Public anger boiled up following days of denials by the military that it was to blame, issued even as Canada and the United States said a missile had brought the plane down.
Riot police fired teargas on Saturday at thousands of protesters in the capital, where many chanted "Death to the dictator", directing their anger at the Islamic Republic's Supreme Leader Ayatollah Ali Khamenei.
"Apologise and resign," Iran's moderate Etemad daily wrote in a banner headline on Sunday, saying the "people's demand" was for those responsible for mishandling the plane crisis to quit.
The latest upsurge in anger adds to public pressure on the authorities, which is struggling to keep the crippled economy afloat under stringent US sanctions.
It launched the bloodiest crackdown in the 40-year history of the Islamic Republic in November after protests against a hike in fuel prices turned political. About 1,500 people were killed in less than two weeks of unrest, three interior ministry officials told Reuters, though international rights groups put the figure much lower and Iran rejected the figure.
'IRAN'S ENEMIES WANT REVENGE'
The Ukraine International Airlines plane was shot down minutes after taking off from Tehran on Wednesday. Many on board were Iranians with dual citizenship, while 57 were holders of Canadian passports.
The downing of the plane came at a time when Iranian forces were on alert for US reprisals following tit-for-tat strikes.
A US drone strike in Iraq on Jan. 3 killed prominent Iranian commander Qassem Soleimani, responsible for building up Iran's network of regional proxy armies in Iraq and beyond. Tehran responded with missile strikes on US targets in Iraq.
No US soldiers were killed in the retaliatory attack, but in the tense hours after that, the Ukrainian Boeing 737 was cleared to take off from Tehran airport and brought down by a missile fired by mistake.
Iranian President Hassan Rouhani said the shooting down of the plane was a "disastrous mistake" and apologised. But a top Revolutionary Guards commander added to public fury when he said he had told the authorities on the same day as the crash that an Iranian missile had struck the plane.
The Guards' top commander, Hossein Salami, said "we are more upset than anyone over the incident", state media reported. Another commander said Iran did not intend to conceal the cause.
But others said Iran's enemies, a term usually used to refer to Washington and its allies, were exploiting the incident.
"Iran's enemies want to take revenge on the Guards for a military mistake," said Ali Shirazi, Khamenei's representative to the Quds Force, the overseas Guards unit that Soleimani headed, state media reported.
'MARCH TOWARDS PARIAH STATUS'
Iranian officials sought to portray the plane disaster as a second blow to a nation mourning after Soleimani's death.
His funeral prompted huge public gatherings, which the authorities described as a show of national unity. But the displays of emotion have been swiftly overshadowed and protesters on Saturday tore up pictures of the slain general.
While both Tehran and Washington have backed off from intensifying their conflict, the leader of Lebanon's heavily armed Hezbollah group called on Sunday for Tehran's allies to begin working to avenge Soleimani's killing.
Retaliation would happen in the "coming days, weeks and months", Sayyed Hassan Nasrallah said in a speech. Iran-allied Hezbollah is designated as a terrorist organisation by the United States.
The killing of Soleimani dramatically escalated tensions between Tehran and Washington, following months of hostilities since Trump withdrew from a nuclear pact between Iran and world powers in 2018 and then toughened up sanctions.
Britain said its ambassador in Iran was briefly detained on Saturday, which Iranian media said was because he was inciting protests. The envoy said he attended a vigil for plane victims.
British Foreign Secretary Dominic Raab condemned the arrest and said Iran "can continue its march towards pariah status ... or take steps to de-escalate tensions" with diplomacy.
