Iran's top Guards commander briefed parliament on Sunday, a day after the armed forces said a Ukrainian airliner was shot down in error in an admission that sparked an angry demonstration.
His closed-session testimony comes after the temporary arrest Saturday of Britain's ambassador to Tehran, Rob Macaire, shortly after he left a vigil for the air disaster victims that turned into a protest.
On the day after the rally at Tehran's Amir Kabir University, tensions appeared to be mounting again on the streets of the capital, with a heavy police presence notably around the iconic Azadi Square south of the centre.
Riot police armed with water cannon and batons were seen at Amir Kabir, Sharif and Tehran universities as well as Enqelab Square. Around 50 Basij militiamen brandishing paintball guns, potentially to mark protesters to authorities, were also seen near Amir Kabir.
The military acknowledged Saturday that the Ukraine International Airlines plane was mistakenly shot down Wednesday, killing all 176 people aboard, after denying for days Western claims it was downed by a missile.
The majority of those on the Boeing 737, which slammed into a field shortly after take-off from Tehran, were Iranians and Canadians, and many were students.
World leaders welcomed Iran's admission, but Canada's Prime Minister Justin Trudeau and others have also called for a full and transparent investigation.
The Kiev-bound plane was shot down at a time when Iran's armed forces were on a heightened state of alert after launching a volley of missiles at US troops stationed in Iraqi military bases.
Iran had vowed to exact "severe revenge" for the January 3 US drone strike that killed Qasem Soleimani, the head of the Revolutionary Guards' foreign operations arm.
- Student protest -
The Guards' top commander, Major General Hossein Salami, briefed parliament about the general's killing, Iran's retaliation and the downing of the airliner, semi-official news agency ISNA said.
At the end of the session, speaker Ali Larijani asked the Majles' security and foreign policy commission to examine the air disaster and how to prevent such incidents from occurring again, ISNA said.
On Saturday, President Hassan Rouhani said a military probe into the tragedy had found "missiles fired due to human error" brought down the Boeing 737.
The Guards' aerospace commander General Amirali Hajizadeh accepted full responsibility.
In the evening, a memorial at Tehran's Amir Kabir University in honour of those killed turned into a demonstration that, AFP correspondents said, was attended by hundreds of students.
They shouted "death to liars" and demanded the resignation and prosecution of those responsible for downing the plane and allegedly covering up the accidental action.
Fars news agency said police "dispersed" them as they left the university and blocked streets, causing a traffic jam.
US President Donald Trump warned Iran against cracking down.
"There can not be another massacre of peaceful protesters, nor an internet shutdown. The world is watching," he tweeted.
"We are following your protests closely, and are inspired by your courage," Trump said in a comment directed at protesters.
The latest demonstrations follow a crackdown on street violence that erupted across Iran over fuel price hikes in November. Amnesty International has said more than 300 were killed.
- Calls for sackings -
Newspapers called for resignations and sackings over the handling of the air disaster.
Sazandegi, a moderate conservative publication, also apologised to its readers for having trusted official sources on the matter.
"Apologise, resign," said the main headline of the reformist Etemad daily.
"Unforgivable," said government newspaper Iran, which published all the names of those who died in the air disaster on the image of black plane tail.
Kayhan, a hardline daily, led on the supreme leader's "strict orders" to follow up on the "painful incident of the plane crash".
As public anger grew, state television aired interviews with people who it said "have not forgotten everything the Guards have done for the country".
Britain's ambassador to Tehran meanwhile took to Twitter to deny he had attended the demonstration before being arrested.
"Can confirm I wasn't taking part in any demonstrations! Went to an event advertised as a vigil for victims of #PS752 tragedy," Macaire said, adding he had been detained half an hour after leaving the area.
"Normal to want to pay respects -- some of victims were British. I left after 5 mins, when some started chanting," he tweeted.
The arrest triggered diplomatic protests, with London calling it a violation of international law and EU foreign policy chief Josep Borrell added his voice to the chorus of condemnation.
"Very concerned about the temporary detention of the UK Ambassador @HMATehran in Iran. Full respect of the Vienna convention is a must. The EU calls for de-escalation and space for diplomacy," Borrell tweeted.
Iran's Mehr news agency said Macaire was arrested for his alleged "involvement in provoking suspicious acts" at the gathering in front of the university.