Wildlife traffickers in Vietnam are using Facebook to sell ivory tusks, rhino horns, and other illegal animal products, according to an undercover investigation from the Wildlife Justice Commission (WJC). As first reported by The Guardian, the investigation found that over the course of 18 months, 51 traffickers in the village of Nhi Khe sold wildlife products worth a total of $53.1 million. The traders use Facebook to sell processed ivory, as well as entire tusks and tiger bone paste. Findings from the investigation were presented at a two-day public hearing that began Monday at the Peace Palace in the Hague.

According to the WJC, traffickers in Nhi Khe use private Facebook groups to sell wildlife products to buyers in Vietnam and other countries across southeast Asia. To reach buyers in China, where rhino horn is prized for its purported medicinal value, they primarily use WeChat. The products sold over the course of WJC's investigation came from up to 907 dead elephants, 225 tigers, and 579 rhinos, representing nearly half of all the rhinos that were killed in South Africa last year. Other products came from pangolins, hawksbill sea turtles and helmeted hornbills.

"The scale of criminality involved simply cannot be ignored."

Nhi Khe has become a hub of wildlife trafficking, thanks in part to its proximity to Hanoi and the Chinese border. The WJC says it has urged the Vietnamese government to crack down on the illicit trade, though little has been done.

"We have offered assistance and worked with stakeholders to encourage the Vietnamese authorities to act, but so far to no avail," Olivia Swaak-Goldman, executive director of the WJC, said in a statement. "The scale of criminality involved simply cannot be ignored."

The report comes amid a worrying increase in poaching, which threatens elephant and rhino populations. Between 2007 and 2014, poachers killed nearly a third of all savannah elephants in Africa, according to a recent report. An international treaty prohibits the sale of ivory from elephants killed after 1989, though few countries have implemented domestic bans.

Facebook has allowed wildlife trackers to reach a wider market; investigation earlier this year found that the site is emerging as a popular platform for selling both wildlife products and live animals. Facebook's community standards prohibit users from using the site to "facilitate or organize criminal behavior that causes physical harm to … animals." WJC says it is working with the company to combat the illicit trade.

In a statement to the WJC, a Facebook spokesperson said: "Facebook does not allow the sale and trade of endangered animals and we will not hesitate to remove any content that violates our community standards when it is reported to us."