The U.S. retains the flexibility to tighten sanctions further in coming months, but Monday's measures will deprive the rulers in Tehran of more cash for their foreign adventures.
"US bullying is backfiring. We stand with them as they call for the regime to respect their human rights and dignity", said US Special Representative for Iran, Brian Hook.
The export of oil and gas is Iran's main source of foreign income, and the loss of even a part of it could be critical, especially in the midst of the economic crisis Tehran is experiencing, which is only getting worse.
He added, "We have iron will to counter sanctions".
The other remaining signatories to the nuclear deal - Russia, China, France, Germany, the United Kingdom, and the European Union - have condemned the USA decision, stressing that the International Atomic Energy Agency (IAEA) confirms Iran's full compliance with the accord. "I don't think that in the history of America, someone has entered the White House who is so against law and global conventions", he added.
Mr Pompeo said more than 20 countries had already cut their oil imports from Iran. Iran has been complying with the most intrusive inspections regime ever devised, as the International Atomic Energy Agency has confirmed 13 times.
"The Iranian people have had 39 years of economic mismanagement". Bloomberg reported on November 2 that India, Japan and South Korea are among those approved, and that China is in discussions on terms but is among the eight, according to two people familiar with the discussions.
He said the Iranian economy was struggling because of the government's "negligence of its own people".
Trump, always ready to bulldoze worldwide agreements, unilaterally withdrew from the deal and imposed a first round of sanctions in August and the second round now.
The rial now trades at 145,000 to the dollar, down from 40,500 a year ago.
This image taken from the Twitter account of President Donald J. Trump @realDonaldTrump, shows what looks like a movie-style poster that takes creative inspiration from the TV series "Game of Thrones" to announce the re-imposition of sanctions against Iran.
Waivers were also issued to allow European firms to continue conversion work on two of Iran's nuclear facilities. However the official list issued on Monday afternoon revealed that not to be the case, asking a number of awkward questions of Iran's neighbour.
His administration also wants to stop what it calls Tehran's "malign" activities - including cyber attacks, ballistic missile tests, and support for terror groups and militias in the Middle East.
Britain said on Monday it regretted the decision to reimpose sanctions on Iran.
The sweeping USA sanctions will be debilitating to the government's day-to-day running of the country.
Washington says the new sanctions are created to pressure Tehran into changing tack.
"The European Union does not approve of it", said European Economic Affairs Commissioner Pierre Moscovici, regarding the sanctions.
United States sanctions permit trade in humanitarian goods such as food and pharmaceuticals, but measures imposed on banks and trade restrictions could make such items more expensive.
Hours before the fresh sanctions went ahead, thousands of people in Iran marked the anniversary of the 1979 hostage-taking at the USA embassy by carrying placards mocking Trump and burning American flags and fake dollars. "[Iran] wanted to take over the whole Middle East". If the Republicans win and maintain control over both houses of Congress-consequently bolstering Trump ahead of the 2020 presidential elections-Iran would have to turn to other options.