Ugandan rebels have withdrawn from peace talks aimed at ending two decades of conflict.
The Lord's Resistance Army says it is boycotting talks with the government because it says Ugandan army troops are surrounding the rebels, in violation of a truce.
The head of the L.R.A.'s negotiating team - Martin Ojul - said late Wednesday the peace process is in grave danger of failure because of the alleged military buildup.
Uganda's military denies deploying troops anywhere near the rebels.
On Wednesday, the army accused rebels of violating a truce by leaving a neutral camp in southern Sudan. A military spokesman said the army would take action to keep the rebel fighters from regrouping.
Hundreds of rebels had assembled at the camp in recent weeks in accord with a truce agreement signed with the government.
The two sides have been meeting in southern Sudan to try to end the rebels' 20-year insurgency. The talks have been clouded by several issues, including the International Criminal Court's refusal to drop war crimes charges against five top L.R.A. leaders.
The rebels are accused of killing, kidnapping and mutilating thousands of civilians during their insurgency.
Some information for this report was provided by AP and Reuters.