PHILADELPHIA (Reuters) - Animal welfare investigators on Monday sought clues in the skinning of 11 puppies whose bodies were found stuffed in a bag left in a ditch in eastern Pennsylvania.

The gruesome discovery was made on Friday in Lower Macungie, about 20 miles from Lynn Township, where days earlier another animal carcass was found skinned and cooked, with its feet cut off, said Bruce Fritch, board president of the Lehigh County Humane Society, which is investigating the slayings.

"It's just heinous," Fritch said.

A black plastic sack containing the skinless puppy bodies was found by a woman walking her dog near a park in Lower Macungie.

The puppies appeared to be no more than 2 weeks old and the only hair left on their bodies was on the paws, although it was such a small amount that investigators were unable to determine the color, Fritch said.

The bodies were taken to a veterinary hospital, where experts attempted to determine the cause of death, he said.

"It's terrible," Fritch said. "Hopefully, somebody saw something and will come forward."

Investigators were conducting DNA tests to determine whether the animal found in Lynn was a dog, a coyote or another animal.

(Reporting by Dave Warner; Editing By Barbara Goldberg and Bill Trott)