Switzerland said on Monday it is holding talks with the USA and Iran about launching a payment channel to help ensure that food and drugs keep flowing to the Islamic Republic. He added that Trump's policy of "maximum pressure will be fully in place as of tomorrow".
To continue exporting crude oil, Iranian tankers in recent weeks have been turning off their transponders to avoid detection.
Later a senior State Department official told reporters that the USA was ready for talks with Iran.
The sanctions cover 50 Iranian banks and subsidiaries, more than 200 persons and vessels in its shipping sector, and targets Tehran's national airline, Iran Air, and more than 65 of its aircraft, the statement said.
Secretary of State Mike Pompeo argued that the new Iran sanctions - going into effect one day before the USA midterm elections - are tough enough to keep the Islamic Republic from pursuing a nuclear weapon. 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.
Secretary of State Mike Pompeo said the waivers, which expire in six months, were necessary to avoid disruption of world oil markets and to give the eight countries more time to eliminate their imports.
His comments came after the United Kingdom suggested it was against Mr Trump's decision to reointroduce the sanctions.
The president did not respond to a question about the waiver.
But while Rouhani's government is working to salvage the 2015 Joint Comprehensive Plan of Action, better known as the Iran nuclear deal, Iranian hardliners appear to be digging in for resistance. "We are prepared to resist any pressure", Rouhani said.
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.
The administration's strategy is to punish Iran so severely that it's compelled to negotiate a permanent end to its nuclear ambitions, as well as what the USA calls its "malign behavior" in the Middle East.
The US expects to have reduced Iranian oil exports by more than 1 million barrels even before Monday's tranche of economic penalties.
US officials said the jurisdictions that had been given waivers would be identified on November 5, although they have not yet been disclosed.
India's oil minister Dharmendra Pradhan confirmed on Saturday that the country, Iran's top oil client after China, had won a waiver from the United States sanctions after a "forceful campaign" by prime minister Narendra Modi.
The deal brought about the lifting of most worldwide financial and economic sanctions in return for Tehran curbing its disputed nuclear activity under United Nations surveillance. "We have the knowledge and the capability to manage the country's economic affairs", Foreign Ministry spokesperson Bahram Qasemi told state TV on Friday.