Mr Zarif said European powers - who say the nuclear deal is working - were asking other countries to continue buying Iranian oil or even start doing so when the next batch of U.S. sanctions take effect.
"These are the most biting sanctions ever imposed, and in November they ratchet up to yet another level".
In several videos posted to social media over the past week, crowds of dissidents are heard chanting, "Death to the dictator" as the United States prepared to reinstate sanctions on the country following President Donald Trump's exit from the worldwide nuclear deal in May.
It involves possible punishments to European companies if they comply with Washington's demands, while offering them a chance to sue the US for interference.
Among large European companies that have suspended plans to invest in Iran are France's oil major Total and its big carmakers, PSA and Renault.
Anti-government demonstrations have spread across the country in recent months, from Iran's heartland to dozens of cities, including the capital of Tehran, as citizens grow increasingly disillusioned by the weak economy, strict Islamic laws, and chronic drought.
The chief executive of reinsurance group Munich Re said it may abandon its Iran business under pressure from the United States, but described the operation as very small.More news: MoviePass slashes plan to three movies per month
Iranian Foreign Minister Mohammad Javad Zarif said Wednesday it was hard to imagine new talks with the United States after it lost the trust of the world with its erratic decision-making. "There is no doubt about this", Khamenei was quoted as saying in comments that appeared only a day after the new USA sanctions took effect.
Mohammad Javad Zarif told the Iran newspaper that President Donald Trump's goal of forcing the rest of the world not to buy Iranian oil was impossible.
Already facing broad economic fallout as their currency implodes, Iranians are wondering how the next phase of the crisis in U.S. relations will play out - and what, exactly, America's long-term strategy is toward their country.
In addition to the labor minister, the Iranian cabinet includes three other economy-related ministers: Finance, Industry and Commerce, and Agriculture.
Signed in 2015, the landmark deal was meant to lift sanctions against Iran in return for curbs in its nuclear programme.
"China has consistently opposed unilateral sanctions and long-armed jurisdiction", the Chinese foreign ministry said in a faxed statement to Reuters, responding to questions on the new United States sanctions and Trump's threats on firms doing business with Iran.
"If you stab someone with a knife and then you say you want talks, then the first thing you have to do is remove the knife", Rouhani said in a speech broadcast live on state television.