According to Reuters, the Trump Administration imposed sanctions against Iranian exports of crude oil.
The move is part of the administration's rejection of an international nuclear accord, which eased sanctions against Iran.
US President Donald Trump chose to abandon the 2015 Iran nuclear deal back in May.
Since then, the US State Department estimates that Iran has lost over $2.5 billion in oil revenue.
Iranian President Hassan Rouhani called the action economic war, while Foreign Minister Mohammad Javad Zarif said the sanctions are bullying Iran and isolating Washington D.C.