Detectives are investigating the discovery of a human body part on open ground.
A passer-by found the remains at The Mayne in Clonee, Co Meath, at around 4.30pm yesterday.
Gardai in nearby Ashbourne were called in to investigate.
The area was sealed off ahead of a technical examination by forensic experts.
The body part remains at the scene and will later be removed to the morgue in Navan, Co Meath.
A Garda spokesman said: "We have no further information at this stage, searches will continue at first light tomorrow morning."
It is understood the body part is a human arm.
It was found in a wooded area.
As it was getting dark at the time of the discovery, detectives decided to postpone a full search until dawn.
Gardai will be hoping that fingerprint or DNA evidence may be able to help them identify the remains.
Clues will be cross-referenced with details on the missing persons database.
A search at daybreak will determine if there are any further remains in the immediate area.