Iran's state-run IRNA news agency says Foreign Minister Mohammad Javad Zarif has resigned.

IRNA cited a spokesman, Abbas Mousavi, confirming Zarif resigned after an Instagram post from the longtime diplomat offered an "apology" for his "inability to continue to his service."

There was no immediate reason offered for what prompted Zarif's resignation.

However, the diplomat was the driving force behind Iran's 2015 nuclear deal with world powers. That deal is now on the verge of collapse after President Donald Trump withdrew America from the accord last year.