A South African military helicopter that was patrolling Kruger National Park Saturday evening, scouting for rhino poachers, crashed, killing five airmen, the army said Sunday.

“The helicopter was on a scheduled aerial patrol of the Kruger National Park as part of Operation RHINO, the anti-rhino poaching operation,” Brig. Gen. Xolani Mabanga said in a statement reported by the AFP news agency.

“A preliminary investigation is currently under way to establish the sequence of events that led to the fatal crash of the helicopter,” he added.

Poaching for rhinoceros in South Africa has been on the rise, with figures from the government indicating a record 668 rhinos killed for their horns in 2012, up almost 50 percent from the figure for 2011.

The majority of the animals were killed in the Kruger park, the country's biggest wildlife reserve, according to a BBC report.

South Africa is home to around three quarters of the world's rhinoceros population of around 28,000 animals. In 2007, a mere 13 animals were lost to poachers, the report said.

So far this year, 188 rhinos have been poached in the country, 135 in Kruger alone, according to the most recent government figure, released last week.

Surging demand for rhino horns from affluent consumers in Vietnam and China, for its supposed medicinal properties, is believed to be one of the reasons behind the increase in poaching. Rhino horns can fetch around $65,000 per kilogram.

It was reported Thursday that three suspected rhinoceros poachers from Mozambique were killed in a shootout with rangers in Kruger National Park.