The government is looking into the possibility of South Korean firms violating UN sanctions against North Korea amid a report that two oil tankers, previously owned by them, were added to Pyongyang's oil smuggling fleet in recent years, a Seoul official said Thursday.

On Tuesday, the Asia Maritime Transparency Initiative (AMTI), a website on maritime security under the Center for Strategic and International Studies, reported on the transfers of the vessels -- the Sin Phyong 5 and the Kwang Chon 2 -- via China.

UN Security Council resolutions prohibit any member states from the "direct or indirect supply, sale or transfer" to the North of "any new or used vessels" unless previously approved by the council.

"Following the report, we began trying to clarify the facts related to the case, as this is a case of the two vessels previously owned by companies of our country. We are looking into specifically when and how those vessels were sold," the official said on condition of anonymity.

"As it has always been with past similar cases, we are examining this case in close consultation with related agencies, such as the oceans ministry in charge of managing such vessels, and the Coast Guard," he added.

It remains unknown whether the South Korean firms were aware that the tankers would ultimately fall into the hands of the North or if they had no inkling of where the vessels would end up.

The AMTI report pointed out that Pyongyang's new acquisition of the tankers follow on from another tanker transfer in 2019, "demonstrating North Korea's ability to draw upon several avenues to continue expanding its oil smuggling capacity despite UN prohibitions." (Yonhap)