Five South African soldiers were killed in a helicopter crash on Saturday while they were on patrol for rhino poachers in the Kruger National Park, the defence department said on Sunday.
A spokesman said the five were taking part in "Operation Rhino", in which the army is trying to stop the slaughter of the animals for their horns, worth more than their weight in gold.
The cause of the crash is under investigation.
On Wednesday, three suspected poachers were killed in a shoot-out with rangers in the vast Kruger, where the killing of the animals has become rampant.
So far this year, 188 rhinos have been poached in South Africa, 135 in Kruger alone, according to government figures released this week.
In 2012, 668 rhinos were poached in South Africa, a 50% rise on the previous year and double the number killed illegally in 2010.
Surging demand from newly affluent consumers in Vietnam and China, where rhino horn is highly prized for medicinal purposes, is behind the onslaught.
South Africa hosts most of the world's white rhino - over 18,000 - and about 40% of the rarer black rhino.
Many of the poachers in Kruger come from poor villages in neighbouring Mozambique. Elsewhere in Africa, the poaching of elephants for their ivory has also been on the rise.