Uganda's Lord's Resistance Army rebel group has suspended its participation in peace talks with the government.
There is little trust between rebels and the army
It says the Ugandan army killed three of its fighters heading towards an assembly point in southern Sudan.
The LRA said its leaders would stay away from the talks until the Ugandan army withdrew from positions east of the River Nile and go back into Uganda.
The faltering peace talks have been taking place in Juba in Sudan in an attempt to end the 20-year insurgency.
A truce has been in place whilst LRA rebels are supposed to gather at two assembly points in southern Sudan.
Tens of thousands of people have died and more than one-and-a-half million displaced during the war as the LRA attacked civilians and abducted children in northern Uganda and southern Sudan.
"We cannot afford to lose our troops whilst we are talking peace," LRA delegation spokesman Obonyo Olweny told the BBC's Focus on Africa.
"The government of Uganda should not use the time of peace talks to prosecute war and achieve military victory," Mr Olweny said. "If they want war, let them come out clearly and say they do not want peace and fighting resumes," he added.
The Uganda army rejected claims that LRA forces were heading towards assembly points saying they were seeking an excuse to explain why they haven't assembled as part of a cessation of hostilities agreement.
"We have not killed any LRA. If anything they are very far away from Ngangala and Magwi as they claim," Army spokesman Major Felix Kulayigye told the BBC.