Tehran called on Seoul to quickly pay $ 6 billion in oil purchases from the country, which was frozen after Washington embargoed it, according to the South Korean newspaper.

The payment request was notified to the Korean Ambassador to Iran last month but so far has not been completed, South Korean newspaper Chosun Ilbo quoted an unnamed official as saying on 14 December. Iranian agencies, including the central bank, also complained about delayed payments.

South Korean officials said Iran expressed "extreme frustration" when Seoul had not paid the oil. The payment has been deposited in two South Korean banks but has not been transferred to Iran's central bank due to US sanctions on the agency.

South Korea sent a delegation to Iran last November and explained that it would cooperate with the United States to complete the transfer of money to Tehran.

In September, the United States issued a ban on Iran's Central Bank, in the strongest sanctions ever taken. Washington accused Tehran of being behind a cruise missile attack, unmanned aircraft entering two Saudi oil refineries, which Tehran denied.

South Korea imports the 5th largest oil in the world. Their import of oil from Iran was halted when the US re-sanctioned Tehran in May, leading to a 46% reduction in trade turnover this year. The ban came after Iran stopped fulfilling some commitments under a nuclear deal signed with major powers in 2015.