Almost 160 rhinos were poached in South Africa in the first three months of this year as trade in the animals' horns drives up the illegal killings, a minister said Wednesday.

"The toll of rhinos poached in South Africa for 2012 has reached the alarming figure of 159, in the midst of the increased anti-poaching effort," said Water and Environmental Affairs Minister Edna Molewa.

"The Kruger National Park continues to bear the brunt of these losses, with the rhinos poached in the park having reached a staggering total of 95," said Molewa at a media event at the iconic reserve.

"This is no longer an environmental management problem only, but it has become a matter in which we have involved all law-enforcement agencies."

A joint force of the country's army, police, special investigators and prosecutors has been set up to tackle the mass killings. Since January authorities arrested 90 suspected poachers.

South Africa would not put up a fence at the park's eastern boundary, which forms the border with neighbouring Mozambique, said Molewa.

"In the end it was concluded that the fence will be too expensive and difficult to maintain. Instead we are now looking at a buffer zone between Kruger and the private reserves/farms in Mozambique."

The animals' distinctive horns are hacked off to be smuggled to the lucrative Asian black market, where the fingernail-like substance is falsely believed to have powerful healing properties.

Last year, a record 448 were poached.

South Africa asked Vietnam to help sniff out poachers, said Molewa.

"We have recently approached the Vietnamese Ministry of Agriculture and Rural Development and asked if they could conduct inspections and verify that the white rhinoceros trophies exported from South Africa to Vietnam are still in the possession of the hunters."