Malaysian authorities have detained two vessels off Johor over suspected unauthorised ship-to-ship (STS) transfer activity.

According to a Malaysian Maritime Enforcement Agency (MMEA) social media post, the agency received information about two vessels operating alongside each other approximately 1.4 nautical miles northwest of Tanjung Buai. The vessels were detained at around 3:20 AM on Wednesday.

The detained vessels were a Malaysian-registered tugboat and a dredger. The tugboat carried five crew members, including Malaysian and Indonesian nationals, while the dredger had 13 Malaysian crew members on board.

During the operation, authorities discovered an oil cargo suspected of lacking proper ownership and delivery documents. Undocumented ST transfers of this kind are a recurring concern in Malaysian waters, where covert cargo transfers are associated with smuggling and sanctions-evasion activity, and the MMEA regularly conducts patrols and detention operations in the Johor area near busy shipping lanes.

The vessels and their cargo, valued at approximately RM260 million ($64.3 million), were detained for further investigation under Malaysia's Merchant Shipping Ordinance 1952 and Customs Act 1967. Under these laws, vessels suspected of undocumented cargo transfers can be seized pending investigation, with penalties for those found responsible. Further details are expected as the investigation proceeds.