Indonesian Navy chief Yudo Margono yesterday defended enforcement action against foreign ships, saying they continue to anchor illegally in his country's waters as they wait to enter Singapore port despite repeated orders not to do so.

He was responding to a Reuters article published on Sunday alleging that more than a dozen shipowners have made unofficial payments of about US$300,000 (S$405,000) a piece to release vessels detained by the navy.

Admiral Yudo said the authorities had to carry out "law enforcement and enforcement of maritime sovereignty" and urged any party making such claims to provide proof of their allegations.

"Please disclose who received the payment… If he were a navy official, state his name, rank and base unit," he told reporters yesterday, on the sidelines of a ceremony marking the 76th anniversary of Indonesia's marine force.

Adm Yudo said the Indonesian authorities have the right to detain any vessel without a permit to enter the country's territorial waters, pursuant to both Indonesian law and the United Nations Convention on the Law of the Sea.

The Reuters report cited a dozen sources including shipowners, crew and maritime security staff involved in the detentions and payments, which they said were either made in cash to naval officers or via bank transfer to intermediaries who told them they represented the Indonesian Navy.

Reuters, however, was not able to independently confirm that payments were made to naval officers or establish who the final recipients of the payments were.

The detentions and payments were first reported by Lloyd's List Intelligence, an industry website.

The Indonesian Navy had earlier told Reuters that there had been an increasing number of ships being detained in the past three months for anchoring without permission in Indonesian waters, deviating from the sailing route or stopping mid-course for an unreasonable amount of time.

"Every time we step up law enforcement, such baseless claims from overseas parties arise. Still, we will also do our evaluation and check if there is any truth to such claims," said Adm Yudo.

The Singapore Strait, one of the world's busiest waterways, is crowded with vessels waiting for days to dock at Singapore.