(CNN) -- Five South African soldiers died in a helicopter crash while patrolling for rhino poachers in the sprawling Kruger National Park.
All aboard the flight were killed in the crash Saturday night, according to a government spokesman.
The soldiers were conducting Operation Rhino, which aims to combat rampant poaching at the park.
"On behalf of government and the entire nation, we wish to express our sincere condolences to the families of these five soldiers and may their souls rest in peace," President Jacob Zuma said in a statement.
An investigation is under way to determine the cause of the crash.
Conservation group Save the Rhino estimates that there are 25,000 rhinos in Africa. Of those, about 21,000 live in South Africa.
A record number of rhinos were killed in South Africa last year, fueled by the belief that their horns can cure cancer.
The unsubstantiated belief on their healing powers is spreading in southeast Asia, sending clients paying top dollar for the horns.
In an effort to combat poaching, South Africa has cracked down on the illegal trade and teamed up with countries that serve as destinations for the rhino horns.
South Africa signed an agreement with China last week to work together to reduce poaching.
So far this year, 188 rhinos have been poached nationwide, 135 of them at Kruger, according to government numbers released last week.
The crash adds to a grim toll for the South African military.
Last week, it lost 13 soldiers in the Central African Republic capital of Bangui, where they were helping the local military quash a rebel uprising.
CNN's Jennifer Deaton contributed to this report