A 10-week-old puppy was kicked to death when it ran up to a group of people in a Cambridgeshire park in what the RSPCA called a "sickening" attack.
The Jack Russell was being walked by its owner, a 15-year-old girl, in Priory Park, St Neots, on Monday.
The puppy ran over to three people in a wooded area of the park, and one of them kicked it in the head. It died almost instantly.
An RSPCA spokeswoman called the attack "absolutely shocking and sickening".
A member of the public tried to resuscitate the puppy but it died from a fractured skull.
The offenders, who ran off, wore hooded tops.
RSPCA inspector Cherry Evans said: "This is an absolutely shocking and sickening incident which caused a great deal of pain to this small puppy, and left her owners devastated.
"It is difficult to understand how anyone could be so deliberately cruel and it is vital that anyone with information comes forward."
Pc Amanda Foreman, of Cambridgeshire police, said: "This has upset an entire family who are finding it hard to understand how someone can do this to a puppy.
"If anyone saw what happened, or knows something about this, they should get in touch."
A man, who wishes to remain anonymous, has offered a £200 reward for information which leads to the successful arrest and conviction of the offender.