President Donald Trump will early tomorrow (AEST) choose whether to scrap the Iran nuclear deal and reimpose sanctions, but uncertainty over his decision has been roiling the Iranian economy and international oil markets for weeks.

Since December, Iran's currency has lost one-third of its value. Foreign investors, who have been jittery ever since Trump took office, have delivered only a fraction of their commitments. And while the Iranian economy has generated 600,000 jobs a year since the nuclear deal took effect in 2016, unemployment is running at an all-time high.