The Arabic-speaking Janjawid militia groups fighting alongside Sudanese government forces against rebels in Sudan's western Darfur province have been blamed for a series of ceasefire violations within Darfur and have now begun terrorising villages across the border in eastern Chad.
Diplomats and Chadian government officials say these cattle raiders equipped by the Sudanese government with modern weaponry need to be reigned in quickly if rapidly souring relations between the desert neighbours are to be salvaged.
However, they question how much control Khartoum has over these nomadic horsemen and whether the Sudanese government has the will or the capability to bring them back under government control.
“Either the Sudanese government does not control the militia and requests international assistance to neutralise the militia and secure the border, or they could do it themselves, but just don’t want to,” Ahmad Allami, President Idriss Deby’s official spokesman, told IRIN.
“Now, there is the feeling that Sudan does not have control over the militia and needs assistance,” he continued.
“I think Khartoum has been overwhelmed by the situation of the militia," one European diplomat in the Chadian capital told IRIN. "They gave weapons to people they do not control and they do not really want to control them either as they might still need them in the future,” he added.
The United Nations is also growing increasingly worried about the activities of the Janjawid.
UN Secretary General Kofi Annan sent a letter to Sudanese President Omar Hassan al-Bashir on Thursday urging him to disarm the militias, whose attacks on civilians in Western Darfur have sent more than 800,000 people fleeing from their villages, many of them across the border into Chad.
Bertrand Ramcharan, the acting UN High Commissioner for Human Rights, told reporters after briefing the Security Council in early May: "One, there is a reign of terror in this area. Two, there is a scorched earth policy. Three, there are repeated war crimes and crimes against humanity. And four, this is taking place before our very eyes."
The scale and frequency of Janjawid incursions into Chad appears to be increasing, threatening the safety of more than 110,000 refugees from Darfur who have sought shelter there and threatening to end Chadian government's official neutrality in the conflict.
So far Chad has been acting as a mediator between the Sudanese government and the Sudan Liberation Army and the Justice and Equality Movement, the two rebel groups fighting against it in Darfur.
Last month, Chadian officials persuaded the two sides to sign up to a 45-day humanitarian truce at peace talks in N'djamena. But the rebels have accused Khartoum and its Janjawid allies of repeated ceasefire violations and African Union ceasefire monitoring team has yet to be deployed on the ground.
The truce was supposed to allow immediate access by relief agencies to the war-affected population of Darfur, but reports of regular ceasefire violations and a growing number of cross-border incidents could endanger its renewal when it expires on 25 May.
Chad's acting Defence Minister, Emmanuel Nadingar, told reporters last week that on 5 May, the Chadian army clashed with a raiding party of Janjawid 25 km inside Chadian territory and killed 60 of them.
One Chadian soldier was killed and seven others were wounded in the battle, he added.
It was the most deadly incident to have been reported between Chadian and Sudanese forces since the Darfur rebellion began in February last year.
“Once more the intervention of our forces was necessary to push them back,” Nadingar said.
“We are in such a situation that we fear our patience could have limits,” he added.
One captured Janjawid fighter who was presented to the press in Chad this week confirmed fears that the militia were operating on their own initiative without necessarily following orders from Khartoum.
“Nobody sent us to Chad,” said Abakora Abbo Sakhairoun, who identified himself as a Janjawid fighter captured by the Chadian army.
“The Sudanese government equipped us with light weapons - kalachnikovs and bazookas - to fight the rebels in Darfur,” he said as he faced the cameras dressed completely in white. “But we take advantage of this to steal cattle in Chad, though we perfectly know that it is not our mission.”
Diplomats told IRIN that there was nothing new about tribal clashes between nomads of Arabic extraction and village farmers belonging to local African tribes in Darfur, but these days they have become much more deadly because the raiders were better armed.
“The Janjawid have kept their traditional values and ways of living. They do the same as they used to: they steal to get. Only this time, their weapons are more sophisticated,” the diplomat, who asked not to be named, told IRIN.
The Janjawid, whose name means "armed horsemen" in Arabic, are nomadic herders of livestock who traditionally carried knives and cutlasses. However, since the Darfur rebellion broke out last year, the Sudanese government has furnished them with powerful automatic weapons and grenade launchers.
Human rights groups and international humanitarian organisations have repeatedly accused the Sudanese government of using the Janjawid to pursue a campaign of ethnic cleansing against the black Muslim communities of Darfur who do not use Arabic as their first language.
In particular they have accused them of waging war against the Zagawa, Fur and Masaalit ethnic communities, which straddle the frontier with Chad.
Chadian President Idriss Deby is himself a member of the Zagawa tribe and he is growing increasingly exasperated at the political violence in Darfur which is now spilling over into his own country.
Besides Janjawid raids, the Chadian authorities also complain about Sudanese military helicopters straying across the border.
“Sudan must control its armed militia and Chad will do its utmost to protect its population,” he warned, during a visit to Congo-Brazzaville last week.
However, the government of Sudan has strongly denied allegations of ethnic cleansing. It maintains that it is simply fighting a rebellion in its eastern territories which must be suppressed.