Six more dead horses have been found in the same shooting that left 15 of the animals mortally wounded and scattered along the hills of eastern Kentucky a week ago, authorities say.

»PREVIOUS COVERAGE: $15,000 reward offered after 15 horses shot to death in rural Kentucky

The animal rescue group Dumas Rescue, which has been assisting police in the recovery effort, confirmed the gruesome discovery of six new carcasses Sunday.

The latest find raises the toll to as many as 21 dead.

Officials have not said when the six new slayings occurred but believe they were a part of the same massacre.

Thirty or more of the horses were known to graze the quiet fields, according to residents who live near the site. At least six of them survived the tragedy, according to reports.

No one in the area reported hearing gunfire.

The Floyd County Sheriff's Office was first called to the horrific scene Dec. 16 near an abandoned eastern Kentucky strip mine in rural Pike County off U.S. Highway 23.

Officials said someone may have used a low-caliber rifle to hunt down the animals.

“It looked like a battlefield for just horses — we counted 15 that we found dead. All 15 appeared to us to have been shot," Floyd County Sheriff John Hunt told local TV station WYMT last week.

Witnesses said one of the dead animals was a yearling that had been shot in the face.

At least two of the other horses were pregnant but miscarried after being slain, according to reports.

Hunt said one of the dead still had grass in its mouth.

Authorities say the remote region is only accessible by ATV offroad vehicles.

Local veterinarians are performing necropsies to determine the official cause of the deaths.

“Seeing them gunned down is … it’s beyond horrific,” said Tonya Conn of Dumas Rescue, which has helped care for the horses in the past and is now helping the police search the woods for the dead animals. "The response across the country to this horrific situation has restored our faith in humanity," the group said in a statement last week on Facebook, where it has been providing regular updates.

Donations have poured in from across the country since the first reports of the tragedy.

The initial reward of $1,500 quickly grew to $15,000 in days. News outlets reported Monday that the reward had reached $20,000.

The Kentucky Humane Society, Kentucky Equine Adoption Center, The Humane Society, Animal Legal Defense Fund, the Helen Woodward Animal Center and local donors have all pledged funds.

The Humane Society of the United States is also offering a $5,000 reward.

Investigators are still pouring over the crime scene to collect more evidence.

Hunt described the shootings as one of the worst cases of animal cruelty he has ever seen.

"This is very inhumane," he said, "and it's a very cruel act of somebody who just apparently had nothing else to do or whatever, just to go back on a strip job and shoot down horses..."

In November, President Donald Trump signed a bill into law making certain types of animal cruelty a federal felony.

»FROM NOVEMBER: Trump signs bill to crack down on animal cruelty

The Preventing Animal Cruelty and Torture Act makes intentional acts of cruelty to animals federal crimes, carrying penalties of up to seven years in prison. The legislation expanded a 2010 law that made creation or distribution of “animal crushing” videos illegal. The Senate unanimously passed the Preventing Animal Cruelty and Torture Act on Nov. 6, two weeks after the House passed it on a voice vote.