The Lord's Resistance Army, once a Ugandan group, has driven tens of thousands from their homes in the Democratic Republic of Congo and Sudan since it launched a campaign of terror at Christmas.
The UN refugee agency (UNHCR) estimates that by the end of January 130,000 Congolese and at least 10,000 Sudanese had been forced to flee.
In addition, the UNHCR reports that an LRA attack on the Congolese town of Aba, population 100,000, resulted in almost the entire population evacuating the town.
It believes that 5,000 people have already crossed into Sudan at the town of Lasu.
This pattern of attacks, all along a 300km (186-mile) stretch of the Sudan-Congo border, follows a co-ordinated offensive against the LRA late in 2008.
On 14 December the forces of three countries - Uganda, Sudan and Congo - attacked LRA bases in Congo.
It was an attempt to kill as many of the LRA as possible and shatter the movement's command structure.
But the operation was hampered by poor co-ordination and the dense forests in this region - ideal cover for guerrilla forces.
According to Capt Deo Akiiki of the Ugandan Army, these operations resulted in almost 50 fighters being captured and more than 150 killed.
The LRA responded as it had done in March 2002, when the Ugandan army launched a massive military offensive, named Operation Iron Fist, against the LRA bases in South Sudan, with the agreement of the government in Khartoum.
In 2002 LRA leader Joseph Kony split up his forces, before bringing them together again and crossing back into Uganda to carry out attacks on civilians on a scale and a brutality not seen since 1995 to 1996.
In December 2008 the LRA repeated this tactic, dividing into small units, some as few as five or six men.
These units launched a series of attacks on an unprecedented scale in towns and villages across northern Congo and South Sudan.
The UN and humanitarian agencies estimate the rebels have slaughtered some 900 civilians since Christmas.
Villages along the border are now empty as people have fled before the LRA atrocities, which have included tying groups of women together before smashing their skulls and killing babies with heated machetes.
One man who witnessed a Christmas Day massacre by the LRA at a Catholic church in Doroma, a town on the border of DR Congo, recalls how the rebels pounced as worshippers gathered for a festive dinner.
"The LRA had guns, but they did not use them," Isador Bashima said. "They used machetes and swords.
"I went with my aunt and uncle. Both of them were killed.
"When I saw the enemies surround us I automatically ran and escaped. I was really very sorry, but I could not stand any longer."
The LRA attacks on ordinary civilians are not simply random acts of brutality, but form part of a concerted strategy.
Firstly, the LRA is too weak to directly stand up to the armies now confronting it.
Reports suggest the rebels may have as few as 1,000 trained soldiers, with the rest made up of children who have been forced into the movement.
Attacking villages proves the LRA is still a viable organisation and puts pressure on Sudan and Congo to return to the negotiating table.
But there is a second - possibly more important - reason for the killings.
It ties up soldiers in attempting to defend the civilians, reducing the number pursuing Kony and his men across the vast area in which they are operating.
According to UN humanitarian envoy John Holmes, the LRA has scattered across 40,000 sq km (15,000 square miles) of dense forests and plains, five times the area they operated in before the offensive.
This includes parts of the Central African Republic.
The border area is now heavily militarised - Congolese on one side and the Sudanese on the other.
They are supported by two brigades of Ugandan troops, around 6,000 strong, which have helicopters at their disposal.
But the government of this region believes the LRA is only able to continue its offensive with outside support.
The deputy governor of the South Sudanese state of Western Equatoria, Col Joseph Ngere, told the BBC that in his view elements in the Sudanese government in Khartoum were supporting the LRA, as they had in the past.
"He had Khartoum's government support in the 1980s," said Col Ngere. "And I think that continues."
"There are elements that still, clandestinely support the Kony movement. I don't have evidence, but this is my belief."
Khartoum has routinely dismissed such allegations.
What sort of man is Joseph Kony?
Col Ngere was on the South Sudanese team negotiating with the LRA over nearly two years, and is one of only a handful of people who know the elusive rebel leader.
"Kony is a cool person and looks like a normal human being," Col Ngere said. "When you meet him there is nothing about him that makes you think he is a murderer.
"But his mind is destabilised. He is not consistent, and changes the course of any discussion very rapidly. He is suspicious of everyone.
"Kony thinks that the strategy of killing civilians will put pressure on the government of South Sudan to reopen peace talks.
"He has much to gain from this strategy. During the talks Kony gets free food and money. His wives and children are transported from Uganda to come and see him. He gets recognition. That is what he wants."
The view that Khartoum's hand is behind the LRA attacks is shared by many South Sudanese troops - an indication of the deep mistrust between North and South Sudan.
The one force in the area that is not involved in this conflict is the United Nations Mission in Sudan (Unmis).
Its mission is to support the implementation of the 2005 Comprehensive Peace Agreement that ended the North-South war.
But the head of Southern Sudanese forces in Western Equatoria, Brig Gen Deng Rok Dit, is critical of the Unmis role.
"Kony is a regional problem and an international problem. He is a terrorist," says the brigadier. "Unmis is not helping us at all. They are not even giving us intelligence. Nothing."