The move by MUFG’s banking unit is likely to force its customers to stop all dealings with Iran because most international trade requires clearing through financial institutions.

US President Donald Trump in May withdrew the United States from a multi-party deal on Iran’s nuclear programme and ordered the reimposition of US sanctions against Tehran that were suspended under the 2015 agreement.

Washington later told countries to stop buying Iran’s crude oil, that nation’s most important export item, by Nov 4 or face financial consequences.

Japan is one of the biggest buyers of Iranian crude, and MUFG Bank Ltd handles the bulk of those imports, industry sources have told Reuters.

The bank has informed customers in Japan about the decision, given that dealings with Iranian financial institutions will be prohibited after a 180-day wind-down period, which ends on Nov 4, the document showed.

MUFG may revise its policy should additional guidance be given by the United States, the bank said in the document.

MUFG did not immediately respond to a request for comment.