The Indonesian coast guard detained two vessels with Singapore flags off Batam island which allegedly did not have proper papers to sail in those waters, officials said.
Vessel BT ASL Glory and an accompanying barge, BG AST 183, were detained on Sunday, according to information made known yesterday. They were spotted sailing towards Singapore near Batam's Tanjung Uncang.
Eight crew members, one of them a Singaporean, were detained and later released, except for the ship's Indonesian captain.
"We caught the ships because they lacked a notification letter showing intent to sail through Indonesian territorial waters," director of Police Coast Guard Hero Hendrianto Bakhtiar told reporters. "We are holding the ship captain. The other crew members have been released and the case is being processed."
The captain faces a possible jail term of up to five years, he added.
Last Thursday, two Singapore- registered boats were caught escorting a tanker travelling through Indonesian waters in the Malacca Strait.
Indonesia's actions came after President Joko Widodo said he would get tough on those trespassing into Indonesian territory, as part of his pledge to revive the country as a maritime power.
Earlier this year, boats caught fishing illegally in Indonesian waters were blown up at sea and their crew jailed.
Action has also been taken against foreign planes. Last October, a Singapore Technologies Aerospace plane used for pilot training was forced to land in Pontianak, West Kalimantan, after it was found to be flying over the country's airspace without the necessary flight permits. The company later paid a 60 million rupiah (S$6,600) fine.
The seven crew members of the two escort boats are still in Batam as investigations continue.
Batam port office head Hery Setiobudi confirmed that the Singapore authorities have asked for an explanation on the detentions.