Donald Trump has issued a strongly worded tweet warning Iran that “the US is watching” following the deaths of 20 people in anti-government protests that are sweeping the country.

Writing on Twitter, the US president also criticized the Iran Deal, an agreement struck by his predecessor, Barack Obama, in which sanctions were lifted against the Islamic Republic in exchange for a guarantee not to pursue the development of a nuclear weapon.

The people of Iran are finally acting against the brutal and corrupt Iranian regime. All of the money that President Obama so foolishly gave them went into terrorism and into their “pockets.” The people have little food, big inflation and no human rights. The U.S. is watching! — Donald J. Trump (@realDonaldTrump) January 2, 2018

READ MORE: 'Trump's support will not be welcomed by Iranian protesters'

Trump’s latest tweet follows a series of other missives over the New-Year period in which he labelled Iran the “Number One State of Sponsored Terror.” He also condemned the restriction of mobile access to social-media platforms like Instagram and Telegram.

Big protests in Iran. The people are finally getting wise as to how their money and wealth is being stolen and squandered on terrorism. Looks like they will not take it any longer. The USA is watching very closely for human rights violations! — Donald J. Trump (@realDonaldTrump) December 31, 2017

Iran, the Number One State of Sponsored Terror with numerous violations of Human Rights occurring on an hourly basis, has now closed down the Internet so that peaceful demonstrators cannot communicate. Not good! — Donald J. Trump (@realDonaldTrump) December 31, 2017

Iran is failing at every level despite the terrible deal made with them by the Obama Administration. The great Iranian people have been repressed for many years. They are hungry for food & for freedom. Along with human rights, the wealth of Iran is being looted. TIME FOR CHANGE! — Donald J. Trump (@realDonaldTrump) January 1, 2018

Meanwhile, a spokesman for Iran’s foreign ministry has hit back at the US president, saying that Trump should focus on his own country rather than tweet about civil unrest abroad.

"Instead of wasting his time sending useless and insulting tweets regarding other countries, he would be better off seeing to the domestic issues of his own country such as daily killings of dozens of people... and the existence of millions of homeless and hungry people," Bahram Ghasemi said, according to AFP.

Speaking to video news agency Ruptly, Tehran resident Saeid Mohseni said that Trump “should never interfere” in Iranian issues. “As far as it is related to him and as far as it is related to us, we make the decisions about our country’s issues. More than that, I think the issues of our own country should be none of his business," Mohseni said.

At least 20 people have been killed and around 450 people arrested since protests began in Mashhad, Iran’s second-largest city, on December 28. Anger over rising living costs, the state of the economy, and allegations of political corruption are fueling the demonstrations, which have now spread to several cities across the country.

READ MORE: 9 more people killed, 100 arrested overnight as nationwide protests in Iran continue – local media

In the latest incidents, six protesters were killed after reportedly attempting to steal guns from a police station in the town of Qahdarijan, according to Iranian state TV, as cited by AP. Two more people were killed in the town of Khomeyni Shahr, with another fatality said to have been a member of Iran’s paramilitary Revolutionary Guard in the town of Najafabad.