Researchers now hope that this method will lead to a crackdown on wildlife crime in two main hotspots in Africa where the vast majority of the killings take place. The illegal trade fuels the killing of some 50,000 African elephants each year and results in 40-50 tons of seized ivory.

Investigators who collected DNA from the tusks of slain elephants and painstakingly looked for matches on the vast African continent have identified two large areas where the slaughter has been occurring on an industrial scale, according to a study published on Thursday.

Samuel Wasser, the author of the study published in the journal Science and the director of the Center for Conservation Biology at the University of Washington in Seattle, said he hopes the study will focus law enforcement efforts and increase international pressure on host countries to crack down on poaching. He suggested donor countries could demand more robust conservation efforts in exchange for development aid.

Tanzania is one of the countries in the eastern region where rampant poaching has been going on for quite a long time. Several other countries in the central and western regions of Africa have also seen elephant numbers decimated considerably.

The dire poaching situation in Tanzania was already illustrated by a recent census, part of a continent-wide effort to count elephants. The result, announced this month, revealed a 60-percent decline to an estimated 43,330 elephants in Tanzania since a 2009 census, according to the Wildlife Conservation Society.

Tanzania's minister for natural resources and tourism, Lazaro Nyalandu, has come out since the census was conducted and said that the country has taken anti-poaching steps, including the hiring of 500 additional rangers, the establishment of an elephant orphanage and an appeal for more help from international conservation groups.

Africa's poaching hotspots

Between 2006 and 2014, more than 85 percent of seized ivory from savanna elephants came from southeast Tanzania and adjacent areas of northern Mozambique, as well as further north in Tanzania's Ruaha and Rungwa wildlife parks, as poachers moved on from depleted killing grounds, the study said. Some DNA samples came from areas north of Ruaha, indicating the hotspot could be shifting toward southern Kenya, it said.

The other poaching hotspot in the past decade is the "last stronghold of forest elephants," a conservation area called Tridom that spans Gabon, Cameroon and the Republic of Congo, Wasser said.

Each hotspot covers about 58,000 square miles (150,000 square kilometers). The study found that most ivory was shipped, or about to be shipped, from a country other than the nation of origin, possibly to mask smuggling routes.

Poachers have also hit hard in an adjacent area in Central African Republic.

In Mozambique, the government seems to be aware of the threat poaching poses to conservation efforts. Cornelio Miguel, the administrator of Niassa reserve, the largest conservation area in Mozambique, acknowledged that the elephants' numbers have indeed dwindled due to the demand for ivory.

"We assessed the elephant population [in November last year] and, according to our provisional data, the number of elephants dropped from 12,000 in 2011 to 4,450 last year."

The consumer end of the ivory trade in Asia is also elaborate, said William Clark, a study co-author and environmental crimes expert at Interpol.

Much of the ivory is carved into jewelry, cigarette holders and seals used to stamp signatures; an item weighing about 30 grams can sell for about $200 (176 euros), he said. A pair of tusks can weigh about 10 kilograms, meaning several hundred ornate items can be extracted from a single elephant's ivory.

China urged to end ivory demand

In the wake of this damning report, Tanzania's tourism minister Lazaro Nyalandu described elephant poaching as a national disaster, and urged China to curb its appetite for ivory.

"We call upon the international community led by China to end its appetite for ivory," Lazaro Nyalandu, told journalists at the launch of an anti-poaching awareness campaign.

Nyalandu said Tanzania's rangers were overwhelmed by the scale of the poaching, though he also said there were suggestions that migration could account for falling numbers at some national parks.

"We have ordered a new elephant census to be carried out in August to validate the results of this latest survey," he said.