The pressures pushed oil prices to a four-year high at the start of October with Brent crude oil selling for more than $86 per barrel.
"We are determined to implement our policy of maximum pressure on Iran".
US sanctions on Iran are set to take effect on November 4, but it is still not clear how big an impact the loss of Iranian oil will make on global supply.
"Mounting perception of a weakening in global oil demand due to increasing tariff issues between the USA and China, while extremely hard to measure, will be maintaining some negative influence in keeping would-be buyers sidelined", Jim Ritterbusch, president of Ritterbusch and Associates, said in a note.
Trump's goal by exerting energy sanctions on Iran was to minimize the country's sources of income in the current economic war against Iran, he said.
NIOC offered a million barrels of crude oil on IRENEX on Sunday, of which 280,000 barrels were traded.
Oil prices were stable on Monday, supported by a bounce in Asian stocks, but analysts said sentiment remained cautious after a plunge in financial markets last week triggered worries that global growth may be slowing. Since Washington aims to cut Iran's oil sales, private Iranian companies can transparently buy and sell the crude through this market.
Turkey calls for Saudi co-operation into Khashoggi probe
A source close to the Saudi Royal Palace told CNN last week that the location of Khashoggi's body was not known to the Saudis. Investigation of the incident suggests a special hit squad came to the consulate to kill Kashoggi and cover up the murder .
This month, according to Reuters, estimates of Iranian crude exports have varied by more than 1 million bpd, which is enough to cover Turkey's oil demand.
"Saudi Arabia's production has reached 10.7 million barrels per day this month and we could increase production to 12 million barrels per day".
Baghdad has been saying that it would abide by the US sanctions on Iran.
Reacting to the announcement, Iran's OPEC governor Hossein Kazempour Ardebili claimed that Saudi Arabia had "no such capacity to bolster its crude output", and it may be seen as a call for the kingdom to "walk out of OPEC".
Prices were pressured as USA inventories were expected to rise for a sixth straight week as other top producers Saudi Arabia and Russian Federation signalled potential output increases.
"Iran's vice president also cast doubt on any further impact of US efforts against his country's oil exports, saying that 'nothing new will happen" on November 4, as the USA has done whatever it could in recent months.
U.S. Treasury Secretary Steven Mnuchin said earlier this month that it would be more hard for Iranian oil customers to get waivers from the sanctions than it was during the Obama administration, and the U.S. would issue waivers, if any, only to buyers that have significantly reduced Iranian purchases.