Malaysian authorities discovered the decomposing remains of another three endangered Borneo pygmy elephants today, deepening a mystery surrounding at least 13 such deaths this month.

The wildlife department in Malaysia's Sabah state is bracing for the possibility of finding more dead elephants in the Gunung Rara Forest Reserve, where an unknown number of the animals roam, said Masidi Manjun, Sabah's environment minister.

Police are investigating suspicions that the elephants were poisoned. Officials have declined to say whether there are any suspects.

A three-month-old elephant calf tries to awake its dead mother at the Gunung Rara Forest Reserve. (Sabah Wildlife Department/Associated Press)

The first 10 known deaths captured wide attention when they were made public this week. Authorities released several photographs of the elephant carcasses and a particularly poignant one of a three-month-old surviving calf that appeared to be trying to wake its dead mother.

"There is definitely a sense of urgency," Masidi said by telephone from Sabah on Wednesday. "We cannot discount the possibility of more bad news."

The orphaned male elephant, nicknamed "Joe" by his rescuers, was transported to a Sabah wildlife park. Officials say he is under observation and appears healthy.

Fewer than 1,500 Borneo pygmy elephants

The WWF conservation group estimates that fewer than 1,500 Borneo pygmy elephants exist. Most live in Sabah, one of two Malaysian states on Borneo island, and grow to about 2.5 metres tall, about 30 to 60 centimetres shorter than mainland Asian elephants.

Known for their babyish faces, large ears and long tails, Borneo pygmy elephants were found to be a distinct subspecies only in 2003, after DNA testing.

Officials are working to have a laboratory analysis of samples from the dead elephants ready "as soon as possible," Masidi said.

Department veterinarians have said the elephants, believed to belong to a single herd, suffered severe hemorrhages and ulcers in their gastrointestinal tracts.