The US has imposed fresh sanctions on Iranian companies and individuals over a recent ballistic missile test.
The new sanctions prevent 11 entities and individuals linked to the missile programme from using the US banking system.
The move came after international nuclear sanctions on Iran were lifted as part of a deal hailed by President Barack Obama as “smart”.
Four American-Iranians were also freed in a prisoner swap as part of the deal.
Among them was Washington Post reporter Jason Rezaian – whom President Obama described as “courageous”. A fifth American was freed separately.
Rezaian and two of the others freed arrived in Geneva from where they were travelling to a US base in Germany.
The US said it had offered clemency to seven Iranians being held in the US for sanctions violations.
Negotiations over the prisoner exchange delayed the US Treasury’s imposition of the latest sanctions – originally intended to be announced in December.