(CNN) Donald Trump on Saturday drew what may come to be seen as the most significant red line of his presidency in a three-part tweet, vowing specific military action against Iran if it "strikes any Americans, or American assets."

"We have ... targeted 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 "if Iran strikes any Americans, or American assets... Iran itself, WILL BE HIT VERY FAST AND VERY HARD," Trump wrote in a series of tweets.

Trump reiterated his warning in a series of tweets early Sunday, saying the United States just spent $2 trillion on military equipment.

"We are the biggest and by far the BEST in the World! If Iran attacks an American Base, or any American, we will be sending some of that brand new beautiful equipment their way...and without hesitation!," he tweeted. "They attacked us, & we hit back. If they attack again, which I would strongly advise them not to do, we will hit them harder than they have ever been hit before!"

Iran is talking very boldly about targeting certain USA assets as revenge for our ridding the world of their terrorist leader who had just killed an American, & badly wounded many others, not to mention all of the people he had killed over his lifetime, including recently.... — Donald J. Trump (@realDonaldTrump) January 4, 2020

....hundreds of Iranian protesters. He was already attacking our Embassy, and preparing for additional hits in other locations. Iran has been nothing but problems for many years. Let this serve as a WARNING that if Iran strikes any Americans, or American assets, we have..... — Donald J. Trump (@realDonaldTrump) January 4, 2020

....targeted 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. The USA wants no more threats! — Donald J. Trump (@realDonaldTrump) January 4, 2020