After months of postponing measures against Iran’s central bank, U.S. President Barack Obama signed an executive order on Monday freezing all Iranian assets in the U.S., including those of the central bank.

In a letter to Congress, Obama wrote, “I have come to the conclusion that the additional sanctions are warranted, particularly in light of the deceptive practices of the central bank of Iran and other Iranian banks,” citing hidden transactions and other loopholes that are exploited.