Joseph Kony, one of the world's most wanted men, is having to move nearly every day as hunters close in on the African guerrilla leader who may now be in Darfur, a top UN envoy said on Friday.

Defectors have also reported that the Lord's Resistance Army chief is becoming increasingly unstable, Abou Moussa, UN special representative for Central Africa, told reporters.

Kony, who launched his rebellion in Uganda 25 years ago, is wanted by the International Criminal Court for war crimes and his global notoriety increased this year through an internet video that has been watched tens of millions of times.

"Contrary to what Kony used to do – that he would stay one month, two months on the ground – he is now moving almost every other day which means the pressure is mounting on him," said Moussa.

"He is moving and they have found traces of where he has settled. People who have defected have provided information on his state of mind," added the envoy.

Kony is no longer ‘very very stable’, said Moussa, head of the UN Regional Office for Central Africa, who is helping to coordinate the international hunt and get more governments to try to trap Kony.

A multi-national force, led by Uganda and helped by 100 US Special Forces, has been chasing Kony in Uganda, Central African Republic, South Sudan and Democratic Republic of Congo. The wanted guerrilla is believed to have a dwindling band of followers, estimated to number between 200 and 500 fighters.

Troops from South Sudan have however been diverted by their country's growing showdown with Sudan, however, while in DR Congo, government forces are hunting another wanted war criminal, Bosco Ntaganda, Moussa said.

The envoy said it was a ‘manhunt’ for a ‘terrorist’ and that the African Union force is serious even if it is not at full strength yet. "As long as it is not dramatic you don't hear about it, but I can assure you things are happening," he said.

For a long time Kony was believed to be in the jungles of Central Africa. "There are so many indications – some are even indicating that he may have crossed into Darfur," Moussa said.

The UN envoy said he had met Chad's President Idriss Deby to secure a promise that the country would detain Kony if he entered Chad. Moussa added that he had asked to meet Sudan's President Omar al-Bashir to get a similar commitment.

The International Criminal Court's chief prosecutor Luis Moreno-Ocampo predicted on Thursday that Kony will be ‘arrested or killed’ this year.

Kony is wanted by the ICC for rape, the mutilation and murder of civilians, as well as abducting and forcibly recruiting children to serve as soldiers and sex slaves.

Moussa said increased commitment by the African Union and the UN Security Council have strengthened the hunt in the last six months, alongside unexpected initiatives such as the Kony 2012 video which has been viewed 90 million times.

While criticized by some governments, Moussa said the video had done a good job drawing attention to the hunt for Kony and that the United Nations had received letters from school children across the United States and Canada.

The hunt for Kony is to be discussed again at the UN Security Council next month when Moussa will unveil a UN strategy for capturing Kony and overcoming the deep wounds caused by his two decade rampage across several countries.

"He has done so many atrocities, forced so many people to flee," that international action has to go beyond capturing Kony.

"We have to respond to the humanitarian needs of the populations, we have to continue to protect civilians, we need to protect and support the defectors.

"And beyond all that we need to be forward looking in terms of development activities when villages and towns are liberated," Moussa said.