Malaysia's wildlife officials inspects the dead pygmy elephant in Gunung Rara Forest Reserve in the Malaysia's state of Sabah on Borneo island, in this picture taken January 23, 2013 and released to Reuters January 29, 2013. (REUTERS/Sabah Wildlife Department/Handout)

Three more rare Borneo pygmy elephants were found dead Wednesday at a protected reserve in Malaysia, bringing the death toll to 13.

Officials at the Gunung Rara Forest Reserve in Sabah state suspect the animals were poisoned. But the motive remains a mystery because all the elephants had their tusks — often sought by poachers — intact.

"My hunch is that there may be more," wildlife department director Laurentius Ambu told AFP. "I don't think it's an accident."

Ten other dead elephants were discovered in recent weeks, all having suffered internal bleeding.

Tests on their digestive systems suggest they died from acute poisoning.

There are fewer than 1,500 Borneo pygmy elephants — the smallest species of elephant — left in the wild, according to the World Wildlife Foundation.

"Frequent and large-scale patrolling is critical to avoid such conflict from happening again," WWF Malaysia director Dionysius Sharma said. "More resources, including manpower, hardware and finances, should be allocated for the department."