Indonesian police are investigating possible links to terrorism after they intercepted a boat carrying more than 28 tonnes of ammonium nitrate.
One captain and five crew were arrested on Tuesday after police intercepted a boat in waters east of Bali.
"We were patrolling and we suspected a boat as it was avoiding us," Husni Syaiful, head of investigations at Bali customs office told reporters on Thursday.
"When we secured (the boat) we found hundreds of sacks."
The men have since told police that they left Malaysia, heading to Sulawesi with 1500 sacks of ammonium nitrate on board the boat.
The colourless crystal substance is widely used in fertilisers and explosives.
After two days at sea, however, the boat leaked and the men had to dump 347 sacks into the water in order to remain afloat.
Agus Setya from the National Police said they were investigating whether the case had any link to terrorism.
He said there were three similar cases of the attempted smuggling of large amounts of ammonium nitrate in April, July and August of this year.
In those cases a total of 166 tonnes were seized.
"They supplied ammonium nitrate for fishermen, for fishing bombs. Is this (recently case) the same motive? We're investigating it. Who behind this?"
Bali customs said the six men were likely to face charges of carrying unreported imported goods.
This carries a maximum of 10 years jail.
