A woman attending a candlelight vigil in memory of the victims of a Ukrainian airliner downed by Iran talks to a policeman following the gathering in front of the Amirkabir University in Tehran, Iran, Jan. 11, 2020.
Image Description A picture taken in Tehran on Jan. 12, 2020, shows local newspapers carrying headlines such as: 'National Mourning', 'Apologize, Resign', 'Unforgivable', 'Great Disaster'... concerning the downed Ukrainian jetliner last week.

U.S. President Donald Trump says he is indifferent about the prospect of talks with Iran after two weeks of back-and-forth attacks and his imposition of fresh sanctions targeting the Iranian economy.

His national security adviser Robert O'Brien told CBS' Face the Nation Sunday morning that Iran is "being choked off," and that U.S. officials see an opportunity to further intensify pressure on the country's leaders and leave them with no choice but to negotiate.

"Actually, I couldn't care less if they negotiate," Trump said in a tweet late Sunday.  "Will be totally up to them but, no nuclear weapons and 'don't kill your protesters.'"

Anti-government protests erupted again Sunday night in Iran for a second day of demonstrations against the military, which first denied and then admitted it mistakenly shot down a civilian Ukrainian plane last week, killing all 176 on board.

"They are lying that our enemy is America, our enemy is right here," one group of protesters chanted outside a university in Tehran.

Videos showed protesters at other locations in the capital and in other Iranian cities.

A woman holds a picture of newlyweds, victims of the crash of the Boeing 737-800 plane, flight PS 752, as people gather to show…
VIDEOS: Iranians Protest Military's Role in Downing of Plane
Hundreds of Iranians protested in several cities around the country Saturday after Iran's Islamic Revolutionary Guard Corps admitted to mistakenly shooting down a civilian Ukrainian plane, killing all 176 on board

Black-clad police, wearing protective riot helmets, massed in iconic Azadi Square south of the city center and at other landmarks. The police were equipped with water cannons and batons and brandished paintball guns, potentially to mark protesters to authorities. But there were no immediate reports of any crackdown on the protests.

In an emotional speech before parliament, the head of the Revolutionary Guard apologized for the missile attack on the Ukraine International Airlines jet and insisted it was a tragic mistake.

FILE - Chief of Iran's Revolutionary Guard Gen. Hossein Salami speaks at a ceremony in Tehran, Iran, Sept. 21, 2019.

"I swear to almighty God that I wished I was on that plane and had crashed with them and burned, but had not witnessed this tragic incident," said Gen. Hossein Salami. "I have never been this embarrassed in my entire life. Never."

U.S. President Donald Trump warned Tehran against attacking the demonstrators.

"To the leaders of Iran - DO NOT KILL YOUR PROTESTERS," Trump said on Twitter. "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!"

Iranian Foreign Minister Mohammad Javad Zarif, on Twitter, expressed "profound regrets" and apologized for the shoot-down of the Ukraine International Airlines jet. But he contended that 'Human error at time of crisis caused by US adventurism led to disaster."

O'Brien rejected Zarif's claim in a Fox News Sunday interview, saying Iran first covered up its actions then claimed the civilian aircraft veered toward a military base. He said Iran needs to investigate the accident, apologize for it, pay compensation to the victims' families and "make sure it never happens again."

On Saturday in Tehran, protesters gathered near universities and called for the resignation of the country's supreme leader, Ayatollah Ali Khamenei, and chanted, "Down with liars!" and "Death to dictator!"

VOA’s Persian News Service reported protests also spread to other areas of Iran, including the country’s third-largest city of Isfahan.  

Saturday's demonstrations came two months after Iran cracked down on massive anti-government protests, brought about by an increase in the price of subsidized gasoline in November. Iran declined to release a death toll at the time, but Amnesty International said more than 300 people had been killed.

Earlier Saturday, Iran's Islamic Revolutionary Guard Corps admitted it mistakenly shot down the Ukrainian International Airline flight earlier this week. 

FILE - Gen. Amir Ali Hajizadeh, the head of the Guard's aerospace division, attends a mourning ceremony for Gen. Qassem Soleimani a day after a Ukrainian plane crash, in Tehran, Iran, Jan. 9, 2020.(Office of the Iranian Supreme Leader via AP)

The downing of the UIA jetliner, a Boeing 737, occurred just hours after Iran launched a ballistic missile attack on Iraqi bases housing U.S. soldiers in response to the U.S. drone attack ordered by Trump that killed Iranian Quds Force commander Gen. Qassem Soleimani.

A team of Canadian officials is due to travel Monday to Iran to work with the families of victims, including identifying remains and repatriating them.  They will also assist in the investigation.

Of the 176 dead, at least 57 were Canadians.

Canadian Prime Minister Justin Trudeau participated in a memorial service Sunday in Edmonton where he expressed sorrow for those who died and said, "This tragedy should never have occurred."

VOA's Extremism Watch Desk and Persian News Network contributed to this report.