Zanganeh added that neither Iranian oil production nor its exports had changed as a result of USA pressure.
Two other sources said South Korea cancelled July loadings of crude and condensate cargoes from Iran as it was uncertain whether the country would receive an exemption from USA sanctions on Iran trade.
"Further declines in USA crude oil inventories and the significant outage in Libyan oil supply are helping to keep a floor under the market", said Harry Tchilinguirian, head of commodity markets strategy at BNP Paribas SA in London. "People are firming up their numbers of how much Iranian oil exports will be lost, and how much OPEC will increase". The contract added 20 cents on Tuesday, and there was no settlement Wednesday due to the US holiday.
Brent crude LCOc1, the global benchmark, was down 76 cents at $76.63 a barrel by 1148 GMT.
A US government report also weighed on prices this week, showing crude stockpiles rose by 1.3 million barrels, while analysts had forecast a decline.
It's unusual being an oil and energy stock trader these days. The American Petroleum Institute, an industry body, was said to report that stockpiles fell by 4.51 million barrels. "The OPEC monopoly must remember that gas prices are up and they are doing little to help... Reduce pricing now!" the USA leader tweeted.
Crude oil is dispensed into a bottle in this illustration photo June 1, 2017.
Trump has been complaining about OPEC at the same time that Washington is piling pressure on its European allies to stop buying Iranian oil.
USA tariffs on $34 billion in Chinese imports took effect as a deadline passed on Friday and Beijing has vowed to respond immediately in kind, setting the two world's biggest economies on a path towards a full-blown trade conflict. The Obama administration had made a similar exception for countries such as India and China, the two largest buyers of Iranian crude, but the new regime under President Donald Trump is expected to be more heavy-handed with the implementation of sanctions when they kick in, largely because of its desire to increase pressure on Tehran for a regime change.