South Korean authorities confirmed that they are investigating an unflagged cargo ship suspected of breaching sanctions on North Korea on Wednesday, following reports it was seized off the country’s southern coast last week.

The ROK government is “closely cooperating with the U.S.” in an investigation into the De Yi cargo vessel over suspicions that it violated the U.N. Security Council sanctions against North Korea, a spokesperson for the ROK foreign ministry told NK News on Wednesday.

The ministry declined to provide further information, citing the ongoing inquiry.