He wrote about this on his page on Twitter.

These Media Posts will serve as notification to the United States Congress that should Iran strike any US person or target, the United States will quickly & fully strike back, & perhaps in a disproportionate manner. Such legal notice is not required, but is given nevertheless!

- Donald J. Trump (@realDonaldTrump) January 5, 2020

“If Iran hits a US citizen or American target, the US will respond quickly and fully, possibly in a disproportionate manner,” Trump wrote.

Earlier, German Foreign Minister Heiko Maas proposed holding a meeting of EU foreign ministers due to the aggravation of relations between Iran and the United States.

On January 3, Iranian General of the Islamic Revolutionary Guards Corps, General Kassem Suleimani, was killed in a rocket attack on the outskirts of Baghdad International Airport.

Iran's supreme leader Ali Khamenei threatened to avenge the killing of Suleimani.

Trump has promised to deliver a “quick and powerful blow” to 52 targets on Iranian territory if the Americans are attacked.

Iranian Foreign Ministry expressed strong protest to the US because of threats of the American leader.