On Friday, the Trump administration announced the restoration of sanctions on Iran's shipping, financial and energy sectors, the second batch of penalties to be restored after President Donald Trump withdrew the USA from the 2015 nuclear agreement in May.
Most global sanctions on Iran were lifted in early 2016 under a deal Iran signed with world powers the year before in which it curbed its uranium enrichment program, widely seen overseas as a disguised effort to develop an atomic bomb.
The Trump administration has said it is confident that "the toughest ever" sanctions against Iran which came into force on Monday will have the intended effect of altering the Iranian regime's behaviour, even as it dodged a question on whether the U.S. has firm commitments from India and China to stop all oil purchases from Tehran within six months.
There are a lot of experts, Chris, that said President Trump's policy wouldn't have any impact because it was just the United States, and other countries weren't participating.
"Petrochemicals are key to our economy, and we stressed that if we're hit by the Iran sanctions, it would pose grave challenges to our whole economy", said the official who spoke on condition of anonymity.
Eight countries who have significantly curtailed their imports of Iranian oil have been granted temporary waivers to allow them to continue importing Iranian oil after the penalties take effect.
Details of the sanctions will be released at a news conference scheduled for 8:30 a.m. ET with Secretary of State Mike Pompeo and Treasury Secretary Steven Mnuchin.
The US side was unmoved. Washington says it wants a new deal with Iran, curtailing its regional interventions and missile programme - demands which have been flatly rejected by Tehran. America should learn that it cannot use the language of force against Iran.
Iran's economy was already suffering from major structural problems - including major banking issues - before Trump walked out of the nuclear deal.
As part of the new round of measures, the White House has warned Iran's customers they must reduce their purchases of oil to zero or face USA penalties, although it has issued 180-day waivers to eight "jurisdictions" that will allow them to continue importing Iranian oil.
Trump administration to reimpose sanctions on Iran
But only time will tell if Iran's regional policy has changed sufficiently to satisfy Trump and achieve his goals. Later, a senior State Department official told reporters that that the US was ready for talks with Iran.
Broader oil markets remain constrained by trade fears and impending oversupply.
The deal had seen most worldwide financial and economic sanctions on Iran lifted in return for Tehran curbing its disputed nuclear activity under United Nations surveillance. "We are prepared to resist any pressure", Rouhani said. "But they're not doing very well", he said, referring to the economic setbacks the country has already faced because of an earlier round of US sanctions.
Iran has dismissed these charges and continues to keep its stand that its nuclear programme is for peaceful purposes.
Part of the explanation lies in the ambiguous position of the United States, which initially insisted that the sanctions were created to reduce Iranian exports to zero barrels, but has since has softened its position.
The latest tranche aim to significantly cut Iran's oil exports - which have already fallen by around one million barrels a day since May - and cut it off from worldwide finance.
Iran's President Hassan Rouhani has vowed to "break" swingeing sanctions re-imposed by the U.S. targeting core parts of the economy.
The U.S. president took to his unhinged Twitter account to post an image (which you can go find for yourself) warning people that "sanctions are coming", and the image made use of Game of Thrones-esque imagery and fonts.
"So the ultimate objective is to pressure Iran to get back to the table of negotiations as per the terms of US President Donald Trump's administration".
India's top banker State Bank of India, which was handling most of the payments to Iran for oil purchases, is now complying with the US sanctions against Tehran, its chairman said on Monday.
The 444-day crisis after the fall of the USA -allied shah transfixed America, as nightly images of blindfolded hostages played on television sets across the nation.