Iran has sent a major cargo of oil to China before the re-imposition of the second round of US sanctions that will be meant to target the country's oil exports.

An unnamed source from the National Iranian Tanker Company (NITC) told Reuters on Friday that the firm had been shipping over 20 million barrels of oil to China’s northeastern port of Dalian.

The oil shipment would later be sold to China or other buyers, he added without specifying further details.

“As our leaders have said, it will be impossible to stop Iran from selling its oil. We have various ways of selling our oil and when the tankers reach Dalian, we will decide whether to sell it to other buyers or to China,” the source said.

Additionally, the latest shipping data provided by Refinitiv Eikon confirmed that so far, a total of 22 million barrels of Iranian crude oil loaded on NITC supertankers are expected to arrive at Dalian in October and November.

Dalian, which hosts some of China's biggest refineries and commercial oil storage facilities, typically receives 1-3 million barrels of Iranian oil each month.

Reports say Iran had previously stored oil at Dalian during the last round of sanctions in 2014 that was later sold to buyers in South Korea and India.

Back in May, US President Donald Trump pulled his country out of the 2015 Iran nuclear deal - technically known as the Joint Comprehensive Plan of Action (JCPOA) - despite objections from other signatories of the accord.

In August, he re-imposed the first round of sanctions on Iran, with the second phase due to come into effect early next month.

The Trump administration has called on all buyers of Iranian oil to cut imports to zero while pressured OPEC to ramp up output in an attempt to bring down prices.

However, the Islamic Republic has played down the impact of the bans and repeatedly dismissed the US threats to slash Iran's oil revenues.

Last week, Vice President Es'haq Jahangiri stressed that Iran has been able to find new partners to buy its oil even though some countries have stopped their purchases.

"America will certainly not be able to reduce Iran's oil exports to zero," he said. "America thinks Saudi Arabia can replace this oil. But right now Iran's oil has reached more than $80 and with half the previous exports we will have the same income as before."

Moreover, Managing Director of the National Iranian Oil Company (NIOC) Ali Kardor said on Wednesday that the US threat to get Iran's oil exports to zero was just a "political bluff."

"The American president has done whatever he can and he knows very well that bringing Iran's oil exports down to zero is a political bluff," he said.