Police have appealed to the public for help after a sheep was killed near Bronllys last week.
The rural crime division of Dyfed-Powys Police is looking into the incident, which took place between 7am and 10am on Friday, February 17.
Police are treating the incident, which took place on private farm land, as livestock worrying.
The dog's owner is yet to come forward.
Livestock worrying is when a dog attacks or chases livestock on agricultural land or is at large in a field with sheep, which can result in significant injury or suffering and in the worst cases such as this, death of the animals involved.
If you have any information that could help police, you can call 101 and quote reference DP-20230217-133.
The Farmers' Union of Wales reminded dog owners last week to keep dogs on a lead and under close control due to the devastating effects of livestock worrying.