Riau Islands Customs and Excise Office head Nasar Salim said Friday that the wooden ship was intercepted by a customs patrol team off the coast of Mapor Island near Bintan on Wednesday.

The crew had intentionally taken a route to avoid patrol boats belonging to Indonesian or Singaporean authorities, he said.

"They had deliberately used a shipping lane with high waves to avoid security patrol boats, but we managed to intercept them near Bintan Island," Nasar told a press conference in Tanjung Balai Karimun.

The chemical material was shipped on board the Indonesian-flagged KM Fungka Sejahtera without required importation documents, he said.

After leaving Pasir Gadang in Malaysia, the wooden boat sailed headed to the South China Sea, Nasar said.

When approaching Natuna Island, the vessel turned toward Java Island, before it was later captured.

The local customs office were questioning the 16 crew members of the wooden boat which was being tightly guarded at the Tanjdung Balai Karimun port.

The office also barred passing ships and people from approaching the boat, to prevent any possible explosions from the chemical material.

Nasar said ammonium nitrate, which can also be used as fertilizer, was classified as an explosive and any imports of the substance must be approved by the Defense Ministry and the National Police.

The explosives were packed in 3,000 25-kilogram sacks, each containing a 34.5 percent concentration of ammonium nitrate.

A further investigation by the customs office, however, found the chemical material contained pure concentrations of the explosive.

"This *concealing of explosives* has lead to suspicion that the chemicals were intended for violent or other dangerous purposes - but it will be up to the police to investigate this further," Nasar said.

"Around 95 percent of the ammonium nitrate imported into Indonesia is used for basic explosive devices," he said.

Explosives smuggling is a punishable crime and carries a jail sentence of up to 10 years.

According to the captain of KM Fungka Sejahtera, identified only initials as HN, the ammonium nitrate was intended for agricultural purposes on Selayar Island, Nasar said.

However, the crew refused to reveal the identity of the "explosive" importers.

Separately, Riau Islands Police deputy chief of detectives Adj. Comr. Wiyarso said his office would investigate whether the case was linked to any terrorist networks in Indonesia.

"We will look into the importer and recipient of the ammonium nitrate.

"However, I can not say whether there is any terrorist link in the case. We will leave this matter to the National Police antiterror unit for further investigation," Wiyarso said.