The USA assassinated Iranian General Suleimani, arguably the second most powerful man in Iran, on 3rd January 2020. This was following weeks of escalating conflict between the US and Iran. The United States President, Donald Trump, tweeted on 4th January 2020 in response to Iran's threats of retaliation that he would target: "...52 Iranian sites (representing the 52 American hostages taken by Iran many years ago), some at a very high level & important to Iran & the Iranian culture, and those targets, and Iran itself, WILL BE HIT VERY FAST AND VERY HARD."
Update 8th January 2020: Donald Trump has now removed his threat, stating "I like to obey the law".