Juba, South Sudan (CNN) -- South Sudan's army battled rebel forces Thursday, a military spokesman said, as negotiators from the warring sides prepared to meet for talks aimed at ending the violence that has pushed the world's newest country toward civil war.
Having sent delegations to the Ethiopian capital of Addis Ababa, the government and rebels are under mounting pressure from African and Western powers to reach a deal to stop clashes that have killed more than 1,000 people and displaced more than 190,000.
But there is no sign of an end of hostilities just yet.
Military spokesman Col. Philip Aguer told CNN that military forces fought with rebels south of the flashpoint town of Bor, the scene of some of the heaviest fighting in the nearly three weeks of violence.
He said the Sudan People's Liberation Army was trying to stop the rebels from advancing on the capital, Juba, about 200 kilometers (124 miles) away.
South Sudan's government tweeted late Wednesday: "Our forces did a partial withdrawal from Bor but are still fighting in the suburbs #SouthSudan."
President Salva Kiir on Wednesday declared a state of emergency for Unity state and for Jonglei state, of which Bor is the capital.
The two delegations sent by Kiir and the rebels' leader, former Vice President Riek Machar, are already in Addis Ababa.
Talks were expected to begin Thursday but, as of early evening local time, had not.
Not all parties have yet arrived in Addis Ababa, according to a representative of the Intergovernmental Authority on Development, an East African trade bloc which has been mediating in the conflict.
However, it is expected all parties will arrive by Friday and formal talks should get under way, the representative, Tigist Hailu, told CNN.
South Sudan's neighbors, Western governments and the United Nations have been scrambling to stem the latest violence in the country, which seceded from Sudan in 2011 after decades of war.
Hilde Johnson, who heads the U.N. mission to South Sudan, said she wanted to see both parties "take a decisive step to cease all hostilities."
"We want to make this day the day that the violence stops," she said at a news conference in Juba on Wednesday.
Kiir and Machar agreed Tuesday to send delegations to Addis Ababa, home of the African Union, for talks after violence in the oil-rich country that began on December 15.
A cessation of hostilities between their forces is expected to top the agenda.
South Sudan's government said Thursday via Twitter: "We are participating in talks because we want peace for our people even though the rebel groups have not accepted a cessation of hostilities."
Johnson said Wednesday it was too early to say if the planned talks were a breakthrough, "but it is a step in the right direction."
The spiraling violence has sparked a humanitarian crisis.
An estimated 194,000 people have been displaced, with about 57,500 people sheltering in U.N. bases across the country, according to the United Nations Office for the Coordination of Humanitarian Affairs.
Peacekeepers are working to protect the camps, but more resources are needed, Johnson said. She appealed for $166 million in aid to help provide families with food and other emergency relief.
The U.N. Mission in South Sudan has voiced concern about what it said was mounting evidence of ethnic-based atrocities across the country.
"There has been killing and brutality; we have seen killing on ethnic grounds. We need to do everything to prevent the cycle of violence," Johnson said, adding that the African Union had set up a a group to investigate human rights abuses.
"I condemn elements on both sides," she said.
The Intergovernmental Authority on Development, an East African trade bloc that has been helping to mediate between the battling parties, has said an independent body is needed to monitor any cease-fire, Johnson said.
Leaders of the bloc warned Friday that they would "take action" to stop the conflict if South Sudan's warring factions didn't lay down their arms.
The fighting began in Juba but quickly spread across the country, with reports of mass killings soon emerging.
Kiir, from South Sudan's Dinka ethnic group, accused troops loyal to Machar, from the Nuer community, of trying to launch a coup.
The two men have long been political rivals, and Kiir dismissed Machar, along with the Cabinet, in July.
Kiir told CNN on Monday that African nations should have acted quickly to help quell the rebel forces.
U.N. forces are patrolling the streets of Juba in order to protect civilians, Johnson said.
CNN's Khushbu Shah, Laura Smith-Spark, Arwa Damon and Yidnekachew Lemme contributed to this report.