An International nature conservancy group of the World Wide Fund for Nature (WWF) is pushing for an investigation into the death of a dozen rare Sumatran elephants in the past three months in Indonesia, local media reported on Tuesday.

"We really regret the death of those elephants. This would not have happened if there were efforts to prevent this in areas prone to conflicts with elephants." Dede Suhendra, WWF Aceh program manager, said on Monday.

The recent spate of human-elephant conflicts highlights the need for the implementation of the Protocol on Conflict Mitigation between Elephants and Humans in Aceh, Dede said. In Aceh alone, five elephants were found dead between March and June -- two in Aceh Jaya in March and May and three in East Aceh on June 2. In Riau, seven elephants were found dead in the Tesso Nilo forests between March and June.

Officials found the most recent dead elephant in Lubuk Kembang Bunga, in Ukui, Pelalawan on June 7. The elephant, a young male, was already a skeleton and was missing its tusks.

The local Tesso Nilo National Park Nature Conservation Office is investigating the death of seven of the rare pachyderms.

"The recent cases of elephant deaths are really worrying, considering it is a drastic increase compared to previous periods. In 2011, there were no reported death of elephants in Tesso Nilo and only two elephant deaths were reported from the entire Riau province that year," Dede said.

The illegal encroachment of people into protected forest is likely behind the rising numbers, Dede said. Close-quarters living with Sumatran elephants often results in elephant-human conflicts that later lead to elephant deaths.

The missing tusks were also a red flag, Dede said.

"There needs to be an investigation into the possibility that some people are making use of the conflict to obtain elephant tusks," he said as quoted by the Jakarta Globe.

The number of Sumatran elephants in the wild has dropped dramatically in the past four years. The International Union for Conservation of Nature has said the species is now in "critical" condition, or one step away from extinction.

There are an estimated 2,400 to 2,800 elephants remaining in the wild, down from the 3,000 to 5,000 reported in 2007.