U.S. Secretary of State Mike Pompeo has said that Washington will decide "in due course" on whether it will extend waivers for countries seeking to import oil from Iran.
The top U.S. diplomat mentioned that the waivers granted to South Korea and seven other countries will expire on May second.
The U.S. has been placing sanctions on Tehran after withdrawing from the 2015 Iran nuclear deal last year.
South Korea is closely monitoring the issue, as the expiry of the waiver would deal a major blow to the local economy.
Korean companies rely heavily on Iranian condensate to produce petrochemical products.