Energy and finance will follow, with companies facing punishment if they continue to do business with Iran, after US President Donald Trump withdrew from a landmark nuclear deal with Tehran.

August 6 will see the re-introduction of auto and civil aviation sanctions, according to the source.

Sanctions in the energy sector, covering oil, gas and petro-chemicals, will follow on November 4.

"There will be the obligation to reduce imports of Iranian crude oil and, in more general terms, sanctions on any commercial operations and transactions of the (energy) sector with Iran," the source said.

On the same day, sanctions will be extended to the financial sector with "a ban on transactions with a certain number of major financial actors, including the central bank" and on the use of messaging systems such as the international banking system Swift, the source said.

Attributions of so-called "General Licence H" allowing subsidiaries of US companies to deal with Iran will be revoked, the source said.

Washington has given companies 90 to 180 days to wind up contracts with Iran and banned them from signing new ones, under threat of sanctions.