Thousands of Iranians rallied in Tehran on Sunday to mark the 39th anniversary of the U.S. Embassy takeover, as Washington restored all sanctions lifted under the nuclear deal.
China, India, South Korea, Japan and Turkey - all top importers of Iranian oil - are among eight countries expected to be given temporary exemptions from the sanctions to ensure crude oil prices are not destabilized.
China denounced new USA sanctions targeting Iran's oil and financial sectors as "long-arm jurisdiction" on Monday and vowed to continue its bilateral trade with the Islamic republic.
More than 20 importing nations have cut their imports of crude oil already, taking more than 1 million bpd off the market, Secretary Pompeo said at a press conference.
The measures described by Washington as "the toughest sanctions ever" follow US President Donald Trump's controversial decision in May to abandon the multi-nation nuclear deal with Teheran.
China, which has been Trump's main sparring partner on the trade front, is Iran's main oil customer.
While now not threatening to resume higher enrichment, in recent months Iranian officials have made a point to threaten that it could resume at any time faster than before.
It offered Iran sanctions relief in exchange for reducing its nuclear development.
Iran's supreme leader Ayatollah Ali Khamenei denounced the measures on Saturday, saying Trump had "disgraced" United States prestige and would be the ultimate loser in the long-running quarrel between the countries. We want to keep our journalism open and accessible and be able to keep providing you with news and analyses from the frontlines of Israel, the Middle East and the Jewish World. "We are watching the Iranian regime with laser focus". "The European Union does not approve of it", said European Economic Affairs Commissioner Pierre Moscovici, regarding the sanctions. "But they're not doing very well", he said.
The sanctions end all economic benefits the United States had granted Tehran for its 2015 nuclear deal with world powers, though Iran for now continues to abide by the accord that saw it limit its enrichment of uranium.
Another signatory to the nuclear deal, China, has said it regrets the re-imposition of sanctions and that its lawful trade with Iran should be respected.
Saudi Arabia raised pricing for the medium and heavy crudes it sells to Asia, a sign that OPEC's biggest producer sees robust demand for the grades as it boosts output to offset the impact of energy sanctions on Iran.
Rouhani then maintained that the country's exports have increased in the past seven months compared to the same period previous year, saying the growth occurred despite the US' attempt to hamper Iran's economic activities.
According to a report by the US State Department, since 2012, Iran has spent $16bn on proxy groups in the region as well as support for Syrian President Bashar al-Assad.
Trump said the deal, approved by predecessor Barack Obama, was weak and flawed in Iran's favour.
Pompeo also said limited waivers had been issued to allow European and other firms to continue conversion work on two of Iran's nuclear facilities.