The Iranian Foreign Ministry said Tehran may lodge a complaint against South Korea if Seoul refuses to pay off its oil debt, saying the country blocked payment to Iran under U.S. pressure. 

Iranian authorities have been demanding payment of some seven billion dollars for oil it sold to South Korea, with the funds seized in the Asian country amid Washington's economic sanctions. 

Iranian Foreign Ministry spokesperson Seyyed Abbas Mousavi warned of legal action over the blocked funds on Sunday during an interview with local media.

The spokesperson said the "master-servant relationship" between Washington and Seoul is the reason that South Korea is submitting to the U.S.' illegal sanctions.

The spokesperson repeated calls on Seoul to unfreeze the money, saying it must be sincere in bargaining with Iran and honoring its commitments. He then said President Hassan Rouhani has recently issued an order to resort to legal procedures to obtain the oil money held in South Korea. 

The spokesperson added that if diplomacy does not yield results and South Korea continues to obey U.S. policies, Iran will summon Seoul's ambassador to Tehran and force the country to pay off its debt through international tribunals.