Secretary of State Mike Pompeo has said the US is imposing the "strongest sanctions in history" on Iran.
In a speech in Washington, America's top diplomat said Iran would be "battling to keep its economy alive" after the sanctions took effect.
He said he would work closely with the Pentagon and regional allies "to deter any Iranian aggression".
Earlier this month, President Donald Trump took the US out of the landmark 2015 Iran nuclear deal.
US sanctions lifted after the 2015 deal will be re-imposed, Mr Pompeo said, and those and new measures will together constitute "unprecedented financial pressure on the Iranian regime".
The older American sanctions prohibited almost all trade with Iran, making some exceptions only for activity "intended to benefit the Iranian people" such as the export of medical and agricultural equipment.
The secretary of state did not say what new measures Washington was contemplating but he described sanctions imposed last week on the head of Iran's central bank as "just the beginning".
Some of Europe's biggest firms who rushed to do business with Iran after the nuclear deal now find themselves forced to choose between investing there or trading with the US.
