A ewe and three lambs have been killed by a dog in Scalby, near Scarborough.
Officers are investigating after the rare Soay sheep were killed on Saturday 6 August 2016. The lambs were just three months old.
Police are urging dog owners to ensure their pets are kept under control at all times.
Dog attacks on livestock result often in death or severe injury, and have a huge impact on farmers and their livelihoods. The message to owners is simple - keep your dog on a lead near livestock, even if they are in a separate field.
Sadly, the sheep killed are from the same flock where five Soay sheep were shot with air pellets and three have since died from their injuries. The incidents are not believed to be connected.
PC Helen Hardie, of Scarborough Police, said: "I am urging dog owners to keep their pets on a lead, particularly in rural areas around livestock. Even the most mild-mannered dog can see sheep, especially lambs, as something to chase and kill.
"Naturally, the owners of the sheep are devastated by this attack."
Officers have spoken to the owner of the dog believed to be involved. The investigation continues.