All three groups, as well as local villagers, killed 14 elephants in the park between April 14 and 27, WildlifeDirect.org said in a statement, citing information from Congo's state conservation agency.

"The upsurge in elephant killings in Virunga is part of a widespread slaughter across the Congo Basin," Emmanuel de Merode, director of WildlifeDirect.org, said.

"(It) is being driven by developments on the international scene: the liberalisation of the ivory trade being pushed by South Africa, and the increased presence of Chinese operators on the ground, who feed a massive domestic demand for ivory in their home country," he said.

Asia is recognised as a major market for poached ivory.

Numbers of Chinese labourers and traders in Africa have risen in recent years, including Congo where China is investing huge sums in mining and has military units serving with the world's biggest United Nations peacekeeping force.

South Africa has long urged a relaxation of the ivory trading prohibition and lifted a ban on elephant culling on Thursday after years of debate on how to control fast-rising populations which have come into conflict with humans.

Congolese General Vainqueur Mayala, the army's top commander in North Kivu, said he had not been informed about the accusation that his troops had killed five of the 14 elephants.

"I will consult with my special services to see how we can find a solution. They will have to carry out an investigation on the ground, but that shouldn't take too long," he told Reuters.

Poaching of gorillas and elephants has long been a problem in Virunga, but April saw a sharp rise in elephant killings, Alexandre Wathaut, provincial director for Congo's conservation authorities in North Kivu province, told Reuters.

The tusks had been hacked from 13 of the carcasses. Six villagers were caught red-handed and detained with the tusks of the 14th, WildlifeDirect.org spokesman Pierre Peron said.

The killings could threaten the viability of Virunga's elephant population, WildlifeDirect.com said.

The park's elephant population shrank by 90 percent between 1959, a year before independence from Belgium, and the most recent survey in 2006, which found there were just 350 left.

Numbers are thought to have fallen further, unlike populations in Botswana, Zimbabwe and South Africa which have flourished since a 1989 ban on international ivory trading.

That ban was extended by nine years last year under a deal that allowed a one-off sale of government ivory stocks.