A tanker, believed to have been used by pirates to siphon 3,500 tonnes of crude oil from oil tanker MT Joaquim on Saturday, has been seized by Indonesian authorities.

Malaysian Maritime Enforcement Agency (MMEA) deputy director-general (operations) Vice-Admiral Datuk Ahmad Puzi Ab Kahar said the tanker was detained about 4pm (Malaysian time) today, in the waters off Dumai, Indonesia.

"The Indonesian authorities have informed us over the vessel's seizure and detention of the suspected pirates," he told Bernama here.

However, Ahmad Puzi said Indonesian authorities were still conducting investigations on the tanker and would identify whether the individuals on board were the pirates involved in seizing the MT Joaquim.

The Singapore-registered MT Joaquim was laden with 3,500 tonnes of crude oil worth RM2.8 million when it was reported missing on Saturday night, while sailing from Tanjung Pinang, Indonesia to Langkawi.

On Sunday, the MT Joaquim with 10 crew members was found 14 nautical miles east off Pulau Rapat, Indonesia after it was released by pirates at 8.55am. However, the cargo was missing.

Ahmad Puzi said the MT Joaquim was now being brought to a location in Malaysia for repairs and MMEA had contacted the company which owned the tanker to conduct investigations.

Navy Chief, Admiral Tan Sri Abdul Aziz Jaafar meanwhile said the operation to hunt down the pirates could not be carried out immediately as it required approval from the Indonesian authorities since the suspects fled to the waters off that country.