Indonesia's Coast Guard has detained two VLCCs allegedly engaged in an illegal oil transfer off Kalimantan province.

National Iranian Tanker Company's 317,400-dwt Horse (built 2008) and the Chinese-operated 306,000-dwt Freya (built 2000) were seized on Sunday.

Coast guard spokesman Wisnu Pramandita said the tankers have been escorted to Batam island for further investigation.