According to AFP, the sanctions will be introduced "later this week."

#BREAKING US to add Foreign Minister Zarif to sanctions list 'later this week': official pic.twitter.com/TGcLqmUkFN

- AFP news agency (@AFP) June 24, 2019

Earlier, US President Donald Trump announced that he had signed a decree imposing sanctions on Iran’s supreme leader, Ayatollah Ali Khamenei.