US President Donald Trump said Tuesday that the United States would react strongly if authorities in Iran started hanging people amid mass anti-government protests across the country.

"We will take very strong action if they do such a thing," he told CBS News in an interview, when asked about hangings potentially beginning on Wednesday.

"When they start killing thousands of people – and now you're telling me about hanging. We'll see how that's going to work out for them," Trump said in a video clip released online.

The interview took place as Trump was in the northern US state of Michigan to visit a manufacturing plant and deliver a speech on the economy.

In his speech, Trump reiterated a message he had posted earlier on social media, that "help is on its way" for the Iranian protesters.

He also said he had cancelled all meetings with Iranian officials until the "senseless killing" of protesters stopped.

An Iranian official said about 2,000 people had been killed in the protests, the first time authorities have given an overall death toll from more than two weeks of nationwide unrest.

US-based rights group HRANA said that of the 2,003 people whose deaths it had confirmed, 1,850 were protesters.

Asked what he meant by "help is on its ‍way", Trump told reporters they would have to figure that out.

On Monday evening, Trump announced 25-percent import tariffs on products from any country doing business with Iran - a major oil exporter. Trump ⁠has also said more military action is among options he is weighing to punish Iran over the crackdown.

Tehran has not yet responded publicly to Trump's tariff announcement, but it was swiftly criticised by China. Iran, already under heavy US sanctions, exports much of its oil to China, ⁠with Turkey, Iraq, the United Arab Emirates and India among its other top trading partners.

The US State Department on Tuesday urged American citizens to leave Iran now including by land through Turkey or Armenia.

Iranian authorities have accused the US and Israel of fomenting the unrest. Iranian security chief Ali Larijani said on X that Trump and Israeli Prime Minister Benjamin Netanyahu were the "main killers" of the Iranian people.

Russia on Tuesday condemned what it described as "subversive external interference" in Iran's internal politics, saying any repeat of last year's US strikes would have "disastrous consequences" for the Middle East and international security.

The protests began on December 28 over the fall in value of the currency and have grown into wider ‍demonstrations and calls for the fall of the clerical establishment. (Agencies)