Jan. 13 (UPI) -- President Donald Trump has announced on social media a 25% tariff on any country doing business with Iran, tightening his financial vice on the Middle Eastern country whose regime has killed hundreds of protesters in the last two weeks.

Trump said, "This order is final and conclusive" in a statement announcing the punitive measure on his Truth Social platform Monday, though it is unclear if the tariff is legal. Nor did the president specify what he exactly meant by "doing business."

The president frequently uses tariffs as both a negotiating tactic and punishment, but those he has imposed during his second term in the White House have been challenged in the courts, as Congress constitutionally controls the nation's taxing authority and delegates trade powers to the executive branch.

The announcement comes as the Trump administration has been publicly contemplating carrying out military strikes against Iran, a country whose relationship with the United States took a precipitous downward turn during his first tour of the White House and again since he returned to the helm of the executive branch last year.

The Iranian regime, led by Supreme Leader Ayatollah Ali Khamenei, has confronted protests that began last month over the country's deepening economic crisis with escalating violence.