Ugandan rebel leaders apparently have missed a deadline to enter a neutral camp as part of their truce with the government.
Sudanese mediators say Joseph Kony and Vincent Otti have not appeared at either of the two designated camps for Ugandan rebels in southern Sudan. Tuesday is the deadline for members of the rebel Lord's Resistance Army to enter those camps, under a cessation of hostilities deal reached last month.
A southern Sudanese monitor says Kony and Otti's absence violates the agreement. But he suggests that mediators may give the rebel leaders an extension.
Southern Sudan's regional government is mediating talks aimed at ending the Ugandan rebels' 20-year uprising. Uganda's government has offered the rebel leaders amnesty from war crimes if they lay down their weapons and stop fighting.
The International Criminal Court has issued arrest warrants for Kony, Otti and three other top Lord's Resistance Army leaders. The rebels are accused of killing, kidnapping and mutilating thousands of civilians during their long insurgency.
Some information for this report was provided by AP and Reuters.