Juba, South Sudan (CNN) -- Rival parties in the South Sudan power struggle will meet Sunday in Ethiopia for peace talks, an official with the regional group promoting the negotiations told CNN on Saturday.
"The actual meetings begin tomorrow morning," said Mahboub Maalim, executive secretary of the Intergovernmental Authority on Development, in a telephone interview from Addis Ababa, Ethiopia's capital. IGAD is an eastern African trade bloc focused on development initiatives.
He said neither South Sudan President Salva Kiir nor his former vice president, Riek Machar, would attend.
"They are not here now, and they will definitely not be here tomorrow," he said. "Their representatives are here, and in direct contact with them. The issues raised here will go to them. If they need to be in attendance, IGAD leadership will pursue them to be here."
U.S. State Department spokeswoman Marie Harf said Saturday night the negotiations are crucial if peace is going to be achieved.
"The parties must use these talks to make rapid, tangible progress on a cessation of hostilities, humanitarian access and the status of political detainees," she said. "We urge the government of South Sudan to uphold its commitments and release political detainees immediately."
The talks will focus on the cessation of hostilities and negative propaganda, the granting of access to monitors and to humanitarian aid workers, and the question of detainees, Maalim said.
The proxy talks in Ethiopia have been attended by special envoys to IGAD; the heads of negotiating teams of the two South Sudanese parties; Maalim; and the ministers of foreign affairs of Ethiopia and Kenya.
No breakthrough came on the first day of talks, despite pressure on Kiir and Machar from African and Western powers to end the conflict.
Mediators met with representatives of both delegations to try to pin down the issues and set out a framework for the talks, Maalim said.
The proxy talks, which involved negotiators from other African nations, continued Saturday.
"Things are going in the right direction," Maalim said, adding that the speed with which the two sides had sent delegations to Addis Ababa was a positive sign.
But as the two sides' teams negotiated, fighting continued in South Sudan, where three weeks of violence has claimed more than 1,000 lives and forced about 200,000 people from their homes.
The State Department further reduced its presence in South Sudan on Friday amid concern over the deteriorating security situation.
About 20 U.S. Embassy staff members were flown out of the capital, Juba, aboard a C-130 aircraft manned by U.S. Marines, according to the Defense Department. Other U.S. citizens in the country have been urged to leave.
Harf told reporters Friday that "even as we draw down our personnel, we continue to be engaged in and strongly support regional and international efforts to bring the violence to an end."
U.S. Secretary of State John Kerry and other senior officials have been in touch repeatedly with leaders in the region and in South Sudan, Harf said. The U.S. ambassador to South Sudan remains in Juba.
The U.S. special envoy to Sudan and South Sudan, Donald Booth, is in Ethiopia for the peace talks, Harf added.
The fighting began in Juba on December 15 but quickly spread across the country, with reports of mass killings soon emerging.
Kiir, from the Dinka ethnic group, accused troops loyal to Machar, from the Nuer community, of trying to launch a coup. The two have long been political rivals, and Kiir dismissed Machar, along with the Cabinet, in July. Machar has denied attempting a coup.
Although the conflict began as a political power struggle, it has taken on an ethnic dimension and includes evidence of ethnically targeted killings, according to the United Nations mission in South Sudan.
Some observers have said both sides may want to gain the upper hand militarily before beginning to discuss a possible cease-fire.
South Sudan is the world's youngest nation, having seceded from Sudan in 2011 after decades of war. However, long-standing tensions have fueled the latest unrest.
Some of the heaviest fighting over the past three weeks has been in Bor, the strategically important capital city of Jonglei state, north of Juba.
Bor's mayor, Majak Nhial, told CNN on Friday that he does not believe the talks will work.
"The rebels are using them to buy time while they are moving forces from the north to the south," he said, showing pictures of mangled bodies and destruction purportedly caused by rebels in his town.
The rebel forces include ethnic Nuer from a militia loyal to Machar. The youths are known as the White Army for the powder they use on their skin as an insect repellent.
"To get the White Army to reach the capital, they must clear the way and Bor stands in the middle," Nhial said.
The mayor said he fears that, if other tribes join the rebel movement, the country will break apart. "It is going to be a disaster for the country," he said.
Military spokesman Col. Philip Aguer told CNN that South Sudan's army was 20 kilometers (12 miles) outside the city of Bor on Friday.
A day earlier, he had said that the Sudan People's Liberation Army was trying to stop the rebel forces from advancing on the capital, about 200 kilometers (120 miles) away.
Kiir has declared a state of emergency for Jonglei state and northern Unity state.
Humanitarian agencies have warned that the estimated 200,000 who have fled to makeshift camps are facing dire conditions, with many lacking clean water and sanitation in makeshift camps.
The fighting in Bor has led as many as 76,000 to seek sanctuary in Awerial, in neighboring Lakes state, according to the U.N. Office for the Coordination of Humanitarian Affairs.
CNN's Samira Said reported in Atlanta and Arwa Damon reported from Juba. CNN's Antonia Mortensen and Christabelle Fombu contributed to this report.