The U.S. re-imposed the oil sanctions against Tehran at the start of the day, a follow-up to President Donald Trump's decision to ditch a 2015 nuclear deal signed by his predecessor, Barack Obama.
The Trump administration has threatened to take punitive measures against countries that purchase Iranian oil and hamper its aim to cut Iran's oil exports to zero.
But it gave waivers to South Korea and seven other nations, according to Bloomberg and Reuters news agencies, with the apparent aim of reducing the impact on the global economy.
