People for the Ethical Treatment of Animals, or PETA, offered Tuesday a $1,000 reward for information leading to the identification of those who killed three elephants on the Indonesian island of Sumatra, media reports said.

The three pachyerm specimens - two adult females and a 1-year-old baby elephant - were found dead over the weekend in Tesso Nilo National Park, a wildlife preserve surrounded by oil palm plantations in central Sumatra, The Jakarta Globe reported.

What is most probable is that the elephants were poisoned as an act of revenge for the destruction of the huts of workers producing palm oil, park director Kupin Simbolon said.

"Those cowardly killers should be arrested and put on trial," the vice president of PETA in Asia, Jasin Baker, said in a statement.

The World Wildlife Fund, or WWF, said early this year that the Sumatran elephant is at risk of extinction during the next 30 years, its classification having gone from "endangered" to "critically endangered" due to deforestation.

The population of Sumatran elephants grows smaller every year in Indonesia due to illegal logging, oil palm plantations and other threats to their habitat. EFE