By Sarah Grainger
BBC, Gulu, northern Uganda
Lord's Resistance Army rebels have broken the terms of a cessation of hostilities agreement signed last month, the Ugandan army says.
Mr Kony's army fought the government for almost two decades
The government and LRA representatives are currently holding peace talks in southern Sudan to end 20 years of conflict in northern Uganda.
Under the terms of the truce the LRA had agreed to assemble at two points in southern Sudan by last week.
But the UPDF says LRA fighters have begun moving away from a camp.
The LRA had been given three weeks to assemble at two points in southern Sudan in return for an amnesty from the Ugandan government.
According to the Ugandan army, 600 LRA fighters had gathered close to one of these designated reception places, at Owiny Ki-bul last week.
But Ugandan army spokesman, Major Felix Kulaigje said there were indications that the fighters had now begun to move west towards the River Nile and were 8km from the reception camp.
Uganda has been in touch with the mediator of this peace process, the government of southern Sudan, to ask them to intervene.
Major Kulaigje said if the LRA continued heading west then the Ugandan army would have no choice but to deal with them.
The deadline for the LRA fighters to gather at Owiny Ki-bul and a second reception centre in southern Sudan expired last Tuesday but it was not clear if all the rebels had complied with this.
There were reports that the LRA leader, Joseph Kony, had arrived at one assembly point but this was never independently verified.
The whereabouts of the LRA rebels has always been key to this conflict.
Joseph Kony had eluded capture or death for two decades by hiding out, not just in northern Uganda but at times in eastern Congo or southern Sudan, sending other representatives to these peace talks.
And despite this peace process there is a good reason for him to stay hidden.
He and three other rebel commanders have been indicted on war crime charges by the International Criminal Court.