The seizure follows that of the Lighthouse Winmore, another oil tanker which Seoul claims supplied fuel products to North Korea in October, in breach of UN Resolution 2375.
Officials seized the KOTI, a Panamanian-flagged vessel, after it was suspected of illegally selling oil to North Korea, maritime authorities told South Korea's Yonhap news agency.
Russian Federation denied the reports on Saturday, saying via its foreign ministry that it "fully observes fully the sanctions regime" against North Korea.
On Thursday, Chinese officials were forced to deny reports that Chinese ships had carried out similar trans-shipments of fuel at sea to North Korean vessels after the United States released images from satellites showing the Rye Song Gang 1 connected to a Chinese tanker by hoses.
The revelation comes days after South Korea said it was holding a Hong Kong-flagged ship and crew members over transferring petroleum products to a North Korean vessel in global waters in October.
"The government has been in close consultations with related countries and ministries to thoroughly implement the sanctions by the UN Security Council", the spokesman said. The Lighthouse Winmore was seized upon re-entering Yeosu on November 24, foreign ministry officials told CNN.
The Sam Jong 2 was one of four North Korean ships that was blocked from global ports by the UN Security Council on Thursday over suspicions of carrying or transporting goods banned by sanctions targeting Pyongyang's weapons ambitions, diplomats told AFP.
The announcement is the second of its kind this week, further highlighting the of use of ship-to-ship cargo transfers banned by United Nations resolutions.
Only four of the ships on the USA list, the ones belonging to North Korea including Sam Jong 2 and Rye Song Gang 1, were blacklisted at a session held on Thursday, as AFP reported. But South Korean officials did not confirm if the Lighthouse Winmore was one of the vessels pictured.
Earlier this month, the USA requested the U.N. Security Council to deny access to ports worldwide to 10 ships suspected of violating trade sanctions on North Korea.
The KOTI's ties to China also seem clear, the tanker is run by companies operating out of Hong Kong and Dalian, two well-known hubs for North Korean sanctions evasion.
The Lighthouse Winmore is one of 10 ships the U.S. has asked the Security Council to blacklist for violating sanctions against North Korea. It is Panamanian flagged.