US President Donald Trump said on Wednesday he had ordered Treasury Secretary Steven Mnuchin to "substantially increase sanctions" imposed on Iran, amid escalating tensions between Washington and Tehran.
He did not give details on the move, which follows weekend attacks on oil facilities in Saudi Arabia that some US officials blamed on Iran. Iran has denied those allegations.
Yemen's Iran-aligned Houthi group claimed the strikes on a Saudi oil field and the world's largest crude processing plant. The attacks disrupted global oil supplies.
Saudi Arabia has said oil production would be fully recovered by the end of the month.
Riyadh has said it would produce evidence linking Iran to the attack.
The White House and the Treasury Department did not immediately respond to requests to comment.
An already-tense relationship between Iran and the United States has worsened over the past year, when Trump withdrew the United States from a nuclear pact with Iran and six other countries saying it did not go far enough, and reimposed sanctions on Iran.