Local residents say Malaysia is establishing a new post near Kayu Mati Island, Nunukan, North Kalimantan, which according to them is located within Indonesian territory.
Imam Basran, a local leader in Nunukan, said the construction of the post, located near the eastern tip of the island, started a few months ago and was still in progress.
Imam said the uninhabited island had been shared between the two countries since the colonial era.
"I once found an [Indonesia-Malaysia] border stake, built by the British [who once occupied Malaysia], in a swamp on the island," he said as quoted by Antara news agency.
Imam said the swamp was located 200 meters from the island's coast, but there was no clue as to whether the stake had been placed with the consent of Dutch forces that occupied Indonesia at the time.
Imam said it was well known that the eastern part of the island belonged to Indonesia while Malaysia owned the western part.
Abdul Wahab Kiak, a former Nunukan regency councilor from the Indonesian Democratic Party of Struggle (PDI-P), also questioned the construction.