South Korea and Iran’s government officials held talks Sunday on the release of a South Korean oil tanker and its crew seized by Iranian authorities, but failed to reach any agreements.

The Foreign Ministry in Seoul and the Iranian government said Monday that First Vice Foreign Minister Choi Jong-kun and his Iranian counterpart Abbas Araghchi held negotiations in Tehran on Sunday on pending issues.  

According to diplomatic sources, Choi strongly called for the swift release of the MT Hankuk Chemi and its 20 sailors seized by Iran's Revolutionary Guard Corps in the Persian Gulf last week.  

Choi also requested that Iran provide substantial evidence on its claims that the South Korean vessel caused "oil pollution" in Gulf waters.  

Iran, on its part, is said to have repeatedly called on Seoul to address the issue of seven billion dollars in Iranian funds that sit frozen in two South Korean banks under U.S. sanctions, stressing that it’s illegal for South Korea to freeze the funds. 

According to a statement released by Tehran, Araghchi said during Sunday’s meeting that advancing bilateral ties can be meaningful only after the frozen funds issue is resolved. 

On Choi's calls for the release of the South Korean tanker and its crew, Araghchi replied the issue is a technical matter that is being handled by Iran's judiciary.