Ahead of the sanctions, South Korea has become the first of Iran's top three oil importers to drop imports to zero after halting purchases in August from 194k barrels in July.
Oil prices have surged to within an inch of $80 (£61) a barrel as Hurricane Florence nears the United States east coast and could climb to multi-year highs by the end of the week, analysts have suggested.
Benchmark Brent crude futures rose 47 cents to $79.53 a barrel, by 1649 (GMT).
With Middle East crude markets also tightening because of the US sanctions against Iran, many Asian refiners are seeking alternative supplies, with South Korean and Japanese imports of USA crude hitting a record in September.
Under the previous round of sanctions on Iran, OPEC's third-largest producer had used this strategy-keeping oil in floating storage off its coasts-when the USA and European sanctions in 2012-2016 cut its ability to export oil.
South Korea has made a decision to comply with US demands to cut oil imports from Iran to zero, becoming the first to do so out of the top three buyers. South Korea says that it continues talks with the US for a possible waiver.
The Economic Times (ET), an Indian daily said Iran now exports about 2 million barrels a day which is already 28% less than what they used to export in April. Eyes will be on Iranian oil import data from China and India who typically import around 500-700k barrels.
Gordon Gray, HSBC's global head of oil and gas equity research, told CNBC: "While we aren't explicitly forecasting Brent to rise to $100 a barrel, we see real risks of this happening".
Brent crude futures have made a firm breach of the descending trendline which has curbed price action previous.
Opec, the Organization of the Petroleum Exporting Countries that accounts for 40% of global production, cut its forecast for oil demand growth next year in its monthly report.
Novak said global oil markets were "fragile" due to geopolitical risks and supply disruptions.
A six-country monitoring committee overseeing the OPEC/non-OPEC supply accord will meet September 23 in Algiers to assess market fundamentals and potentially make output policy recommendations.
Iran's September exports are expected to plunge and "average as little as 1.5 million barrels a day in September according to the preliminary loading program, compared to around 2.8 million barrels a day of oil exports in April and May", Amrita Sen, chief oil analyst at Energy Aspects, said in a note to clients, carried by Bloomberg.