"Let this serve as a WARNING that if Iran strikes any Americans, or American assets, we have targeted 52 Iranian sites... 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," Trump said via Twitter on Saturday.
"The USA wants no more threats!" added the president, who said the number corresponds to the 52 US diplomats and citizens taken hostage in the storming of the US embassy in Tehran in 1979, after which diplomatic relations between the countries were severed, Efe news reported.
Trump believed that "Iran is talking very boldly about targeting certain USA assets" in response to the death in Baghdad of Soleimani and the vice president of the Iraqi Popular Mobilization Forces, Abu Mahdi al-Muhandis.
On Friday, however, the president said he had ordered the death of Soleimani, commander of the Quds Force of the Islamic Revolutionary Guard Corps considered a hero in the country, in order to "stop a war," not start one.
The Trump administration has argued that the goal of killing Soleimani was to prevent an "imminent attack" that would have endangered the lives of US forces and diplomats in the Middle East, a region in which 60,000-70,000 US troops are deployed.
Trump again held Soleimani responsible for the death on Dec. 27 of an American contractor in an attack against a military base in Iraq and said the Iranian commander also orchestrated the assault on the US embassy in Baghdad, which occurred in response to US bombings in Syria and Iraq.
Iran has promised "harsh retaliation" and in response, the US was to send 3,000 to 3,500 extra troops to the Middle East, US media reported Saturday.
Trump's decision caused stock market crashes, oil price rises and aroused fear among US allies of armed conflict.
Internally, Democratic opposition lawmakers have condemned Trump for not informing Congress beforehand of the attack.
Meanwhile, protests were held in more than 70 US cities from Los Angeles to New York to protest the killing of Soleimani and the sending of more troops to the Middle East, according to the Act Now to Stop War & End Racism anti-war coalition, who spearheaded the demonstrations with other organisations.
Protesters held signs saying "Stop bombing Iraq," "US troops out of Iraq" and "No war or sanctions on Iran."
( With inputs from IANS )