The dredgers operate exclusively between Malaysia and Singapore, transporting “sea sand in bulk”, representatives for the vessels told Jakarta-based media, Bernama reported.

One of the ships is believed to be Malaysian-owned. Yesterday, the Indonesian weekly Tempo reported that the two vessels, MV Yang Cheng 6 and MV Zhou Shu 9, displayed the flags of Malaysia, Singapore and Sierra Leone.

According to sources familiar with the matter, both vessels hold all the necessary permits and approvals for their operations between Malaysia and Singapore.

They said the international automatic identification system, which tracks the movements of marine vessels minute-by-minute, would prove that neither vessel has sailed or transited in Batam waters at any time.

The ships’ representatives said allegations that either vessel had illegally extracted sand from Indonesian waters were fabricated.

The dredgers were detained by Indonesian authorities on suspicion of conducting illegal dredging and dumping in the waters off Batam and the Riau islands. The dredgers were carrying 10,000 cubic metres of sand, according to local news media.