The 3.7-metre-long and 65-centimetre-wide object was fished from the ocean on Monday about 10 kilometres from the popular tourist island of Gili Trawangan, West Nusa Tenggara, the navy said.

A 28-year-old fisherman immediately reported the unusual find to the local authorities, who retrieved it.

“The Indonesian navy will promptly carry out an in-depth examination… of the device to determine its origin, function, and the data contained within it,” navy spokesman Tunggul, who like many Indonesians has only one name, told AFP.

“The Indonesian National Armed Forces will remain fully committed to safeguarding the sovereignty and security of Indonesia’s territorial seas from all forms of unauthorised activities, including the use of underwater devices or equipment by unauthorised parties in Indonesian waters.”

Mataram naval base chief Asep Tri Prabowo told reporters Wednesday the object was under strict supervision and would be sent to Jakarta for further investigation.

An initial examination by the West Nusa Tenggara Police’s bomb squad confirmed it did not contain any explosive or radioactive substances, he added.

Indonesian media reported that lettering on the object suggested it may have been manufactured by the China Shipbuilding Industry Corporation. It appeared to be a device to measure the speed of currents.

This was not the first time a foreign object has been found in Indonesian waters.

In 2021, a fisherman discovered a seaglider in the Selayar Islands, South Sulawesi that the military suspected was being used for oceanographic research.