Iran said it had so far been able to sell as much oil as it needs and urged European countries opposed to US sanctions to do more to shield Iran.
The Russian diplomat says the sanctions go against worldwide law and practices, and that the US government's "policies of issuing an ultimatum and making unilateral moves are unacceptable these days".
Oil prices slipped on Tuesday as concerns that an economic slowdown may curb fuel demand growth overshadowed the reintroduction of sanctions on Iran.
"While the Iranian sanctions should still be viewed as a latent bullish consideration capable of limiting much additional price slippage, it would appear that the Iranian factor alone will not be capable of spurring higher prices without major assistance from a renewed strengthening in the equities, sustainable weakening in the USA dollar or a significant cut back in OPEC production", Jim Ritterbusch, president of Ritterbusch & Associates, said in a note.
U.S. Secretary of State Mike Pompeo said the sanctions already had cost Iran the sale of over 1 million barrels of crude oil a day.
The US on yesterday reimposed all penalties that had been lifted as part of the 2015 Iranian nuclear deal as the Trump administration added almost 700 targets, including 50 Iranian financial institutions, to a sanctions list.
Trump told reporters on Sunday that the sanctions are the strongest ever imposed by the US.
Industry estimates suggest Iran's oil exports have fallen 40 to 60 percent since Trump said in May he would reimpose sanctions. Iran is its third-largest supplier after Iraq and Saudi Arabia and meets about 10 per cent of total needs.
"We've said for a long time: Zero should mean zero", John Bolton, White House National Security adviser told Fox Business Network in an interview.
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Iran's Foreign Minister Mohammad Javad Zarif says new American sanctions are an "indiscriminate assault" on his country.
It also appeared that the USA, in another first, was directly sanctioning the Atomic Energy Organization of Iran, the government agency that oversees Iran's nuclear program.
Mr Pompeo said, these countries showed significant reduction in oil purchase from the Persian Gulf country after the Trump administration reimposed sanctions on Tehran. The President did not respond to a question about the waiver.
On the supply-side, oil is in ample availability despite the sanctions against Iran. "I don't want to lift oil prices".
At the same time, the trade dispute between the United States and China is threatening growth in the world's two biggest economies.
"These sanctions have already had an enormous impact".
Some of the eight countries - China, India, Greece, Italy, Taiwan, Japan, Turkey and South Korea - include OPEC (Organization of the Petroleum Exporting Countries) member Iran's top customers.
These are also Iran's biggest buyers, meaning Iran will be allowed to still export some oil for now. "The market was previously overly focused on the number of countries receiving exemptions on imports from Iran". Watch the efforts that President Trump's policies have achieved.