Bhubaneswar, May 7 (IANS): Poachers have struck again in Odisha's Simlipal National Park with carcasses of four more elephants, apparently poisoned, recovered from the reserve, officials said Monday.

The incident has underscored the need for more efforts to protect the tuskers. In the last five years, more than 60 elephants have been killed -- six this year.

While bones and skulls of three elephants, probably a male, a female and one calf, were dug out close to each other in the core area of the park, that of a baby elephant was found about a kilometre away.

All appeared to have been buried and covered with leaves. The decomposed body parts were dug out by workers this week after a May 3 tip.

"The baby elephant might have been poisoned 20-25 days ago. However, the other three could have probably died three-four years ago," Anup Kumar Nayak, director of Simlipal National Park, told IANS.

The exact cause of the deaths, and the day when they died, would be known after deoxyribonucleic acid (DNA) and other tests, said Nayak.

Experts believe poachers poisoned all the elephants.

The park is located in Mayurbhanj district, some 320 km from here. Simlipal is home to about 450 elephants.

The park covers 2,750 sq km, of which 303 sq km is the core area. This biosphere reserve is also a wild life sanctuary and one of country's first Project Tiger reserves.

The latest development has come as a shock for wild life experts who have stepped up efforts to take adequate measures to prevent poaching as carcasses of elephants are being found in the park frequently.

"During past five years at least 60-70 elephants must have been killed in Similipal by poachers," Biswajit Mohanty, secretary of the wild life society of Odisha, told IANS.

"This year alone at least six recorded deaths of elephants have been reported," he added. "More dead elephants might be found if we conduct a thorough search."