Rebel fighters return to a rebel camp in Jonglei State, South Sudan, on February 2, 2014. Picture: Goran Tomasevic

Addis Ababa - South Sudanese rebels said they would boycott the next round of peace talks starting in Ethiopia on Monday unless the government freed political prisoners and sent home the Ugandan troops who have been supporting it.

The Addis Ababa talks, which secured a ceasefire last month, are intended to end a conflict that has claimed the lives of thousands of people and displaced more than half a million South Sudanese since it broke out on Dec. 15.

The rebels, lead by former vice president Riek Machar, said they wanted four remaining political prisoners held by the Juba government to be released and the Ugandan army, which has been backing President Salva Kiir, to withdraw from South Sudan.

“We are hereby informing all parties ... that we are abstaining from participating in the next round of peace talks, which are scheduled to take place in Addis Ababa today,” the rebels said in a statement.

The said they had evidence that the Ugandan army was “still actively engaged in combat” despite a ceasefire, and accused Kiir's forces of besieging a United Nations compound housing displaced people in Juba.

Both sides have in the past accused each other of wanton killings and ethnic-based reprisals.