"We will not obey such sanctions," Turkish President Recep Tayyip Erdogan said, adding that his government saw Washington's move as "violating the global balance."
The crown prince has threatened to develop nuclear weapons if Iran is able to do the same.
"U.S. bullying is backfiring," Foreign Minister Javad Zarif warned earlier on Monday.
The "people's food basket has shrunk, except for the profiteers of sanctions," said one civil servant living in Tehran.
The U.S. announced that China, Greece, India, Italy, Japan, South Korea, Taiwan and Turkey would be granted a six-month exemption from sanctions on buying Iranian oil.
"We are in the economic war situation," Iranian President Hassan Rouhani warned as new U.S. sanctions took effect. "We are confronting a bullying enemy."
Iran can't afford to show weakness and has no reason to believe Trump will deal honestly with it even it backs down. Besides, Iran is far from the most urgent threat to the United States.
President Donald Trump has gone to economic war with China, giving Russia a chance to further consolidate its ties to a fellow U.S. foe.
The U.S. announced on Tuesday new sanctions against Iran Tractor Manufacturing, the largest tractor manufacturer in the Middle East, and Iran's Mobarakeh Steel Company, the largest steel producer in the region.
North Korea has long been critical of South Korea's dependence on the U.S. despite a historic warming of ties between Cold War-era foes.
"U.S. sanctions against Iran will both weigh on Iran's oil production prospects in the medium term and reduce Iran's crude exports in the short term...," the report predicts.
India is defying U.S. sanctions by buying Russia's S-400 surface-to-air missile system and is increasing its imports of Iranian oil.
On the nuclear deal, Germany sides with Iran against the U.S. and Israel, but it is wary of Tehran's other ambitions across the Middle East.
The 1955 friendship treaty was signed two years after the U.S. overthrew Iran's democratically elected Iranian prime minister and decades before the 1979 Islamic Revolution.
Turkish President Recep Tayyip Erdogan criticized President Donald Trump's policies as "pressure and blackmail."
Secretary of State Mike Pompeo and national security adviser John Bolton spoke at the 2018 United Against Nuclear Iran summit.
Senior officials from Bahrain, Israel, Saudi Arabia, the United Arab Emirates, the U.S. and Yemen spoke at the 2018 United Against Nuclear Iran summit.
Although the economy has remained strong despite sanctions, JP Morgan warned Trump not to get overly optimistic.
The European Union's foreign policy chief said the other nations would "protect the freedom of their economic operators."
Russian foreign minister says his country is trying to distance itself entirely from the U.S.-dominated international financial system and urged others to do the same.
Putin says his country is impervious to threats from the West. But new U.S. sanctions aim to upend that claim. Washington's new mood: "Punish Russia as hard as possible."
Finance ministers of Germany, France and the U.K. have been working together to move the plan forward.
The order is designed to deter foreign interference in upcoming midterm elections and authorized sanctions on countries and individuals caught interfering.
"You get up in the morning, drink your coffee and read the paper. You look at a story and say, So is this the moment in which we've become fascist or isn't it?" Israeli actor Itay Tiran said.
Decades of U.S. sanctions have led Cubans to become inventive with their prophylactics.
After the U.S. defense secretary said Iran was "on notice," the Islamic Republic's top general warned any attacking forces would "pay a heavy price."
The IAEA stated that its observers had access "to all the sites and locations in Iran which it needed to visit" under the agreement's framework.