The admission came after days of vehement denial from the Islamic Republic, which angered Iranians and triggered a public backlash. Videos on social media showed mass protests and people chanting: "Death to the dictator," referring to Iran's Supreme Leader Ali Khamenei.

Demonstrations have spread across Iran since Saturday, after the Iranian regime admitted that its armed forces had unintentionally shot down a Ukrainian passenger plane departing from Tehran, killing all 176 people on board.

"National Security Adviser suggested today that sanctions & protests have Iran 'choked off', will force them to negotiate," Trump said on Twitter Sunday, in both English and Farsi. "Actually, I couldn't care less if they negotiate. Will be totally up to them but, no nuclear weapons and 'don't kill your protesters.'"

President Donald Trump tweeted on Sunday that he "couldn't care less" if Iran negotiates with the U.S. or not, and again warned the Iranian regime not to "kill" its protesters.

The more you give them credit, the more you give them support, the worse it will be for them, because in that case, the regime will consider it is an international plot.

However, Cedomir Nestorovic, professor of geopolitics at the French ESSEC Business School in Singapore, cautioned that Trump's solidarity with protesters may not be good for them.

"I don't believe that President Trump's intervention in this field would be very fruitful for the United States, because it is an internal protest," Nestorovic told CNBC's "Street Signs" on Monday.

"The more you give them credit, the more you give them support, the worse it will be for them, because in that case, the regime will consider it is an international plot, that the United States are intervening in the local affairs of Iran, so I don't think it's a very good thing," he said.

Earlier, Trump warned the Iranian government that the "world is watching," and told the people of Iran "I've stood with you since the beginning of my Presidency, and my Administration will continue to stand with you."

Tensions between the U.S. and Iran reached new heights after the U.S. killing of a top Iranian military commander, Qasem Soleimani, on Jan. 3. His death triggered retaliation from Tehran which responded by firing ballistic missiles at Iraqi air bases housing American and coalition troops. There were no reported casualties in that attack.

However, Iranian armed forces bracing for counter-attacks from the U.S. accidentally shot down the plane killing all aboard including Iranians, Canadians and Ukrainians, which led to public outcry and unrest. Iran has previously been accused by rights groups for clamping down on protests with brute force.

Trump's Sunday tweet was referring to comments by White House national security advisor Robert O'Brien, who told Fox News on Sunday: "I think the maximum pressure campaign is working ... Iran is being choked off, and Iran is going to have no other choice but to come to the table."

O'Brien was speaking about the Trump administration's renewed sanctions on Tehran. Often referred to by Washington as the maximum pressure campaign, it is aimed at crippling the Iranian economy with sanctions that were reintroduced after the U.S. pulled out of a multi-nation nuclear deal with Iran in 2018.

"What's going to cause them to negotiate is the pressure on the economy, and when you've got students out there chanting 'death to the dictator,' and when you have thousands of Iranians out protesting in the street, that's the sort of pressure that's going to bring them to the table," he told Fox News.