Armed gangs killed four rhinoceroses Wednesday in Kenya, selling their horns for profit in illegal markets. This event is possibly the worst poaching incident Kenya's seen in 25 years, the spokesman for Kenya Wildlife Service said Friday.

Sub-Saharan Africa has seen a rise in poaching recently, as armed criminal gangs are killing elephants for tusks and rhinos for horns. These rare materials are usually shipped to Asia for ornaments or medicine. More valuable than gold or platinum, a kilogram of rhino horn could be sold on many Asian black markets for around $65,000, Reuters reported.

Kenya has recently become a major transit point for ivory traveling from east and central Africa to Asia. However, "Kenya has started using high-tech surveillance equipment including drones" to track both poachers and the herds they prey on within its vast national parks, Reuters said.

Wednesday's animal poaching occurred at the private Ol Jogi ranch near Nanyuki, 120 miles north of Nairobi. The poachers escaped with three of the rhinos' eight horns, according to KWS spokesman Paul Muya. The bodies were found at two sites on the ranch.

One conservationist told Reuters he believes it's the worst poaching raid in Kenya since five white rhinos were killed in Meru Park in 1988. National police are meeting with KWS officials to discuss Wednesday's incident, Muya said.

Including the four from Wednesday, 22 rhinos have been killed in Kenya this year, leaving only 1,037 in national parks and private wildlife conservancies, Muya said. Last year, poachers killed 59 rhinoceroses.

Killings like this are why representatives from 160 countries met in late June in Nairobi to discuss the importance of adding illegal wildlife trafficking to global development goals.