Representatives of the rebels and the government of South Sudan on Tuesday held their first meeting aimed at ending a civil war in the country.
The two sides, which signed a peace agreement in August, met in the capital, Juba, in the hope of forming a transitional government of national unity.
The government and rebel factions have been holding peace talks on and off since shortly after the conflict began in mid-December 2013. Several cease-fires agreed to in the past two years were violated.
President Salva Kiir and rebel chief Riek Machar have repeatedly accused each other of cease-fire violations, but both say they remain committed to the August 26 agreement, despite missing every listed deadline.
The United States said Tuesday that it welcomes the return to talks, and added that "many important but difficult decisions remain." Washington called on both parties to cooperate "in the spirit of unity and compromise" to implement the reforms outlined in the peace agreement.
South Sudan is the world's youngest country, winning independence from Sudan in 2011. Conflict erupted after a power struggle between Machar, an ethnic Nuer, and Kiir, from the dominant Dinka group, and the fighting has been especially brutal on civilians.
Both sides are accused of having perpetrated ethnic massacres; recruiting and killing children; carrying out widespread rape and torture; and forcibly displacing populations to "cleanse" areas of their opponents.
The war has killed tens of thousands of people and displaced more than 2 million from their homes while pushing parts of the population into famine conditions.