Two sheep have suffered "severe" injuries and another has died following a dog attack near the Clywedog Reservoir.
Police officers say they are appealing for witnesses to come forward.
The livestock worrying incident happened on private land near the B4518 sometime between Saturday, August 29 and Monday, August 31.
A Dyfed-Powys Police's Rural Crime Team spokesperson said: "We've been dealing with another livestock worrying, dog attack incident today.
"Sadly one ewe lost her life and these two suffered severe injuries".
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