KRUGER NATIONAL PARK, South Africa — They used to rely on snares, poison and shotguns to kill rhinos for their horns. Now international crime syndicates are arming poachers with night-vision goggles and AK-47 assault rifles as the price for rhino horn surpasses gold.

When the crackle of gunfire signals the death of yet another rhino, radios squawk to life here in South Africa's flagship Kruger National Park and soldiers ready for pre-dawn patrols.

"They've become very aggressive," Ken Maggs, head of the South African government environmental crime investigation unit, said of the poachers. "They leave notes for us written in the sand, warnings. That indicates it is an escalating issue ... They are coming in prepared to fight."

The government of South Africa, home to 90 percent of the rhinos left on the continent, is fighting back. Since more than 140 troops were deployed in April, the number of rhinos killed in Kruger has dropped from 40 in March and 30 in April to 15 in May and just two in June. Fifteen alleged poachers also have been killed this year, and nine suspects wounded in gunfights.

Still, rhino carcasses with mutilated faces are becoming a common sight in African wildlife parks. The hacked-off horns are destined to be smuggled to China and Vietnam, where traditional medicine practitioners grind them up for sale as alleged cures for everything from fevers to arthritis and cancer.

The horns have become so valuable that thieves this year started stealing rhino exhibits in European museums. The going rate is up to $44,000 a pound (60,000 pounds a kilogram) according to the London Metropolitan Police department.

Even in the United States, police in Denver have arrested members of an Irish syndicate trying to smuggle rhino horn.

"Aside from Central and South America, every region of the world appears to be affected by criminals who are fraudulently acquiring rhinoceros horns," warned John M. Sellar, enforcement chief of the Convention on International Trade in Endangered Species.

"Government officials are being corrupted. Money-laundering is taking place," he said.

Kruger sprawls across 2 million hectares — about the size of Massachusetts — and around two-thirds of poachers come on foot across the border from Mozambique. Lt. Col. Bongie Vilakazi says the poachers have reacted to the South African army presence by traveling in much larger gangs of up to seven people.

"They come across around sunset, aim to shoot the rhino before dark and then spend the night in the bush before heading home with the horn," Vilakazi said.

Soldiers do not patrol at night though because of the dangerous nocturnal predators: Once, a pride of lions charged at troops in the back of an open van transporting meat, Vilakazi said. The soldiers fired into the air to frighten away the lions. Now they use closed vehicles and live on canned rations.

South Africa's troops are concentrated in 16 temporary bases in the Sabi River valley where two-thirds of rhino killings have occurred.

Park rangers said the deployment has hugely boosted their coverage.

"Before, we were four rangers trying to cover 87 square kilometers (35 square miles), which is nearly impossible," said Cpl. Reckson Mashaba, speaking at a tent camp covered with camouflage netting where he and other soldiers fall asleep to the roar of lions.

Soldiers have been issued high-caliber rifles — in case they need to shoot an elephant or rhino in self-defense, Brig. Gen. Koos Liebenberg said.

The South African military also has set up spy cameras, but Maj. Gen. Barney Hlatshwayo said they need equipment to feed photos in real time so soldiers can respond immediately.

Rhinos have been near extinction before. There were about 100,000 black rhinos in the 1960s, but they were hunted and poached until just 2,400 remained in the 1990s. Conservation efforts have nearly doubled their numbers, but they remain a critically endangered species.

A century ago, there were only about 50 white rhinos left. Now, there are about 20,000, thanks to conservation, relocation to safer regions and many more wildlife refuges and ranches.

But poachers killed 333 rhinos in South Africa last year. And the toll for the first six months of this year is 218 and likely will top 400 at the current tempo, according to Maggs, the head of the government environmental crime investigation unit.

Conservationists have failed to persuade traditional Chinese medicine practitioners and consumers that rhino horn has no medicinal value. Some link the upsurge in rhino poaching to a 2007 Chinese government decision to promote traditional medicine as alternative medicine grows increasingly popular in the West as well. Until then, South Africa was losing about 10 rhinos a year to poachers.

Trophy hunting in South Africa is compounding the problem. More than 100 white rhinos were killed under permit here last year. The Department of Environment did not respond to questions about permits issued this year.

So tempting are the rewards that veterinarians and game ranchers — the very people supposedly dedicated to conserving wildlife — have been arrested in recent months for alleged involvement in the rhino horn trade.

Yet the National Parks department continues to sell wildlife, including rhinos, to game ranchers.

Two Vietnamese citizens were arrested in January in illegal possession of rhino horns killed on a legal hunt.

Police working with tax officials last month arrested a Thai man believed to be a syndicate leader, along with five alleged Thai hunters accused of using legal hunting to illegally acquire horns. Permits are needed to export one trophy horn per hunter. The horn has to be mounted by a taxidermist.

South Africa also has been criticized for exporting young rhinos to China. Conservationists fear they will be farmed for their horns but China denied any such plans. Still, suspicions remain and South Africa last year halted live rhino exports.

Some say the war can never be won and believe the only way to save the species is through legalizing the rhino horn trade.

"If farmers were making a profit out of rhinos they would have the will to guard them against poachers," said rancher John Hume, owner of the largest number of privately held rhino in the world. "Instead, they are siding with the poachers because a rhino is worth more dead than alive."

He said some farmers "just contract with an illegal dealer, shoot the rhino, bury the body, take the horn. It pays him to kill it."

Game ranchers have taken to giving quotes for rhino hunts depending on the weight of the horn, he said, though for Westerners the quote still comes according to the length. At its source, rhino horn is selling in South Africa for about 10,000 rand a kilogram ($670 a pound), Hume said.

As the price soars abroad, some countries are asking why they cannot use a massive stockpile of rhino horns to finance conservation.

Africa has at least 55,000 pounds (25,000 kilograms) of rhino horn under government and private ownership, with 90 percent held in South Africa, Zimbabwe and Namibia.

Zimbabwe, where top-ranking military and government officials are accused of profiting from rhino poaching, said in February it would ask CITES for a special dispensation to sell some of its stockpile.

Conservationists warn that a similar sale of elephant tusks in the 1990s only whetted people's appetite for ivory and led to a surge in elephant poaching.

"This is an emergency. We're at war here," said Joseph Okori of the World Wildlife Fund.

Associated Press writer Donna Bryson in Johannesburg contributed to this report.