The warning came just days ahead of the US re-imposition of all US sanctions on Iran that had been lifted under the 2015 nuclear deal, which will take effect at midnight tonight and cover Iran's shipping, financial and energy sectors.

Speaking to reporters, Mnuchin was quoted by Reuters as saying that "SWIFT is no different than any other entity," adding "We have advised SWIFT that it must disconnect any Iranian financial institutions that we designate as soon as technologically feasible to avoid sanctions exposure."

The Trump administration has been pressuring allies to cut Iranian oil imports to "zero" next month although on Friday the US agreed to grant exemptions to 8 countries that import Iran oil; the countries include Japan, India, and South Korea according to Bloomberg. China, the leading importers of Iranian oil remains in discussions with the US on terms but is among the eight, as is Turkey which will likely receive an exemption, the country's energy minister said on Friday. The full list of countries receiving waivers will be released on Monday.

By cutting Iran off from SWIFT, Iran would lose its ability to be paid for its exports and to pay for imports. Washington has been pressuring SWIFT to cut Iran from the financial system as it did in 2012 before the nuclear deal. Six years ago the EU imposed sanctions on Iranian banks, forcing SWIFT, which is subject to EU laws, to cut financial transactions with at least 30 of Iran's financial institutions, including the central bank.