Zaire -- Purple wildflowers and weeds now shroud the unmarked mass graves. The once grisly dump trucks cart mounds of garbage, not corpses. And at the last count, 976 rickety bars and brothels, plus hundreds of shops and restaurants -- even a hotel -- were doing a brisk trade in the giant refugee camps.


But nearly four months after the world watched in horror as an estimated 50,000 Rwandan refugees collapsed and died in miserable camps on the bleak volcanic landscape, frustrated United Nations officials and relief workers say the largest, fastest international relief effort in history has become a new kind of nightmare.


Their concerns range from massive theft of donated food and other relief goods, to death threats against UN field officers and aid workers, to daily political assassinations and other murders in the three largest camps.


But perhaps most disturbing, humanitarian groups now openly acknowledge that the distribution of relief supplies to the estimated 750,000 Hutu refugees has come under the direct control of former Hutu government leaders and militias -- the same extremists accused of systematically slaughtering at least half a million Tutsi civilians inside Rwanda before they fled in July.


"The militias and the military totally control the camps," said Samantha Bolton, spokeswoman for Medecins sans Frontieres, once one of the most active of the 85 aid groups here.


"It's outrageous," she said. "It's gotten to the point where we're aiding and abetting the perpetrators of genocide."


The ethical questions and misgivings have grown so severe that MSF announced Tuesday it was withdrawing its last workers from camps around and 15 other international aid groups -- including CARE, Oxfam and the American Refugee Committee -- have publicly threatened to halt assistance unless security is assured.


The extent of the problem took time to surface. At first, with cholera raging and thousands dying daily, relief agencies gave little thought to who controlled the camps.


But Jean Lapierre, CARE's coordinator, said security quickly deteriorated as the emergency abated. And in late September, he said, fighting broke out between rival gangs known as the Bandits and the Scouts.


"It was really like the Bloods and the Crips, fighting for turf," Lapierre explained, referring to Los Angeles gangs. The two-day gang war ended with the disappearance, and presumed deaths, of 30 Scouts. But the Bandits' reign at Katale was short-lived. Leaders of the Hutu government in exile quickly asserted control in the camp and created a sinister security force called La Jeunesse, or The Youth, to enforce their edicts. Working in groups of 20, the young toughs patrol the camp's 11 zones.


The new leaders demanded complete control of distribution of relief goods, even the blankets, plastic sheeting and other non-food items that were given to "vulnerables" -- the aged, pregnant women, children and the disabled.


UN officials now estimate that 30 to 50 percent of the refugees do not get enough food or other assistance. Aid workers fear the food is given to the estimated 30,000 Rwandan soldiers who are regrouping and retraining in nearby forests, or is being sold to buy arms.


Just down the road from Katale, for example, the black market at Rubare is bustling. Roadside stalls are stacked with four-quart cans of refined vegetable oil and bulging sacks of corn and flour, all clearly marked "USA -- Not to be Sold or Exchanged." On sale nearby are heaps of gray blankets and other relief goods.


The diversion of food has led to a dramatic increase in malnutrition in the camps.


Nicola Dahrendorf, acting director of UN refugee agency in Zaire, said the number of children treated for severe malnutrition had doubled in the last six weeks.