Trump who ordered the killing of Soleimani without giving prior information to Congressional leaders, said in the dramatic tweet on Sunday that he was not legally required to notify Congress.
"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 and fully strike back, and perhaps in a disproportionate manner. Such legal notice is not required, but is given nevertheless," the President tweeted.
Yale Law School Professor Oona Hathaway tweeted: "This tweet threatens to break several laws. The President cannot notify Congress under the War Powers Resolution by tweet".
In an earlier tweet, Trump threatened the destruction of 52 Iranian targets, including cultural sites.
"Wait, when he says 'These Media Posts'..... Is he talking about his Tweets? So is he too scared or lazy to talk to Congress," replied a user.
Under the "War Powers Act" of 1973, the US President is required to notify Congress within 48 hours of deploying US military assets into combat, said media reports.
Soleimani, 63, who was killed in the January 3 US drone strike was the elite Quds Force chief in charge of Islamic Revolutionary Guard Corps operations outside Iran, and has been on the ground in Syria and Iraq supervising militias backed by Tehran.
Trump has used Twitter to issue surprise orders, announcements, and even threats against other nations like North Korea.
In 2018, Trump fired Secretary of State Rex Tillerson via a tweet.
Despite threatening war on the platform, Twitter is unlikely to take any action against Trump.
In January last year, the micro-blogging platform declared that "blocking a world leader from Twitter or removing their controversial tweets would hide important information".
( With inputs from IANS )