Iran announced Tuesday its first arrests over the accidental shooting down of a Ukrainian passenger jet, as protesters vented their anger over the catastrophic blunder for a fourth consecutive day.
Nearly two weeks after the US killed a top Iranian commander in Iraq, tensions with the West increased further as EU countries on Tuesday launched an arbitration process charging Tehran with failing to observe commitments in the 2015 nuclear deal, prompting Iran to warn of unspecified "consequences".
The Ukraine International Airlines plane was brought down by a missile shortly after takeoff on Wednesday, killing all 176 passengers and crew on board.
Iran has struggled to contain the fallout over its handling of the air disaster, after initially dismissing Western claims it was brought down by a missile before admitting it on Saturday.
The tragedy has seen hundreds of angry protesters, most of them students, take to the streets, apparently chanting slogans against the Islamic republic.
New videos circulating on social media purported to show fresh protests on Tuesday evening at universities in Tehran, along with clashes between students and Basij militia loyal to the establishment.
It was not possible to immediately verify the videos.
Earlier, AFP correspondents said around 200 mainly masked students gathered at Tehran University on Tuesday and were locked in a tense standoff with youths from the Basij.
"Death to Britain," women clad in black chadours chanted as Basij members burned a cardboard cutout of the British ambassador to Tehran, Rob Macaire, after his brief arrest for allegedly attending a demonstration Saturday.
Kept apart by security forces, the groups eventually parted ways.
AFP journalists said there appeared to be a lower police presence on Tuesday compared to preceding days.
Internet connectivity was significantly lower than usual.
- 'Real rift' -
The protests have been much smaller than nationwide demonstrations against fuel price hikes that turned deadly in November.
But one commentator said the latest rallies showed there was a "real rift between the people and the authorities".
"I hope that (police restraint) will continue and that no lives are lost, because this could be a catalyst for more protests," Mehdi Rahmanian, director of reformist daily Shargh, told AFP.
In another sign of growing dissent, a group of artists cancelled their participation in the Fajr festival, held each year on the anniversary of the 1979 Islamic Revolution, according to Hamshahri newspaper, which is owned by Tehran City Hall.
Meanwhile, group of reformist journalists in Tehran published a statement denouncing the lack of freedom of the press and official media.
"We are attending the burial of public trust", said the statement, which the official IRNA news agency reported on.
Even a key state TV personality, Elmira Sharifi, hit out at authorities on Twitter.
"At a time when you should come and give your apologies and explanations, you stay quiet! Why are you bringing us shame in front of the public?".
Tehran had for days denied Western claims based on US intelligence that the Boeing 737 had been downed by a missile.
It came clean on Saturday when Revolutionary Guards aerospace commander Brigadier General Amirali Hajizadeh acknowledged a missile operator had mistaken the plane for a cruise missile and opened fire independently.
Judiciary spokesman Gholamhossein Esmaili said the first arrests had been made over the air disaster, without naming them or specifying how many.
"Extensive investigations have been carried out and some people have been arrested," he said.
Esmaili also said around 30 people had been arrested in the protests over the air disaster.
- 'World watching' -
The announcement came shortly after President Hassan Rouhani said -- in relation to the air disaster -- "anyone who should be punished must be punished".
"The judiciary must form a special court with a high-ranking judge and dozens of experts... The whole world will be watching," he said.
"It cannot be that only the person who pressed the button is at fault. There are others."
The Kiev-bound plane was shot down at a time when Iran's armed forces were on heightened alert after launching a volley of missiles at Iraqi bases hosting US troops.
Iran fired the missiles in retaliation for a US drone strike on January 3 that killed Qasem Soleimani, the head of the Guards' Quds Force foreign operations arm.
Addressing that issue, Rouhani said while "the root of all sorrows goes back to America... this cannot be a reason for us not to look into all the root causes" of the air disaster.
The president also demanded officials explain why it took so long for authorities to announce the real cause of the air disaster.
But Rouhani said that for him it would be more important that Iranians are "assured that this incident will not be repeated".
Iran has invited experts from Canada, France, Ukraine and the United States to take part in the probe.
The office of Ukraine's President Volodymyr Zelenskyy said he spoke to Canada's premier Justin Trudeau on Tuesday for a third time since the crash, with the latter asking for help from Kiev in liaising with Iranian authorities to help identify bodies of Canadian citizens.
Also on the diplomatic front, Britain on Monday summoned Iran's ambassador to lodge its "strong objections" after its Tehran envoy, Macaire, was temporarily arrested for allegedly attending a demonstration on Sunday night.
Iran's judiciary spokesman on Tuesday described Macaire as a "persona non grata" and said his "obligations under international treaties are clear".