RABAT, Morocco >> At least 68 elephants, some 4 percent of the population of one of Africa’s oldest parks, have been slaughtered by poachers over the last two months using chain saws and helicopters, the non-profit group managing the park has warned.

The Johannesburg-based African Parks group said that since mid-May, the 5,000 square kilometer (1,900 square mile) Garamba National Park in Congo, which was established in 1938, has faced an onslaught from several different bands of poachers.

One particular sophisticated group is shooting the elephants with high powered rifles from a helicopter and then taking off their tusks with a chain saw. They are removing the elephants’ brains and genitals as well.

African Parks, which runs seven parks in six countries in cooperation with local authorities, said the poachers also include renegade elements of the Congolese army, gunmen from South Sudan, and members of the Lord’s Resistance Army, a militant rebel group whose fugitive leader Joseph Kony is an alleged war criminal. 

"The situation is extremely serious," Garamba park manger Jean-Marc Froment said in the statement. "The park is under attack on all fronts."  A 2012 census found just 2,000 elephants in Garamba Park, down from 20,000 in the 1960s.

In one skirmish with poachers, park guards had to try to protect themselves against hand grenades thrown by Southern Sudanese poachers, some wearing military uniforms.

Froment singled out in particular elements of the LRA, which is notorious for its kidnapping children and using them as soldiers, and has been active in the park.

In recent years, the U.N. has warned that armed groups in Africa have been turning to ivory poaching to fund their struggles. Many are also using the more sophisticated weapons that flowed from Libya after the fall of Moammar Gadhafi in 2011.

Conservationists say a thriving ivory trade market in Asia is helping fuel the worst poaching epidemic of African elephants in decades. 

The Geneva-based Convention on International Trade in Endangered Species of Wild Fauna and Flora said Friday that 20,000 elephants were killed in 2013, but the overall poaching was on the decline due to better law enforcement.