An opening ceremony for the second round of the talks was held late Tuesday in Addis Ababa.
Both the government of South Sudan and Toby Lanzer, the U.N. humanitarian coordinator for South Sudan, said in separate tweets that the talks had resumed.
The official opening of the second round of peace talks will take place shortly at the Hilton hotel in Addis Ababa #SouthSudan— Gov of South Sudan (@RepSouthSudan) February 10, 2014
Good news from Addis: the second round of talks on #SouthSudan have begun. I wish the negotiators well. Reconciliation & peace are vital.— Toby Lanzer (@tobylanzer) February 11, 2014
At the talks' opening ceremony, the lead mediator for the Intergovernmental Authority on Development (IGAD), Ethiopian diplomat Seyoum Mesfin, had harsh words for the two sides in the conflict, which has claimed thousands of lives and forced nearly one million people from their homes.
Seyoum said the writing was on the wall that "things were not going well" in South Sudan, but the country's leaders failed to take action.
"The gaps between the demands of the people on the one hand and what the government was able to deliver was wide," Seyoum said.
"Disillusionment with corruption and inadequate governance was high. The leadership failed to see this and to respond with a coherent policy and visible commitment to address the issues of peace, security and development in a coordinated way," he said.
The talks appeared to be in jeopardy until the last minute as opposition negotiators said they would not take part unless certain conditions were met.
The key pre-conditions that they set was that political detainees whose release was supposed to be expedited by all sides after the first round of talks, were allowed to attend, and that foreign forces pull out of South Sudan.
After receiving reassurances from IGAD that seven former detainees "would be attending tomorrow," the opposition agreed to return to the negotiating table, Goi Jooyul Yol, a spokesman for the anti-government side at the talks, said.
This second round of talks is supposed to address root causes of the fighting in South Sudan as well as nation-building and reconciliation.
The chief negotiator for the opposition, General Taban Deng Gai -- who the government of South Sudan has accused of treason for his alleged role in what President Salva Kiir said was a botched coup bid on Dec. 15, that set off weeks of violence around the country -- said the government had not complied with the agreements signed in the first round of negotiations.
One agreement signed last month called for an immediate cessation of hostilities while the other called for the government and opposition to expedite the release of 11 political figures who were detained in South Sudan at the start of the weeks of violence, to allow them to take part in the talks when they resume.
"Of the 11 detainees, only seven were released while four are still behind bars. This is another very serious violation of the cessation of hostilities," Deng said.
The government has accused the four of plotting with others, including former vice president Riek Machar and Deng, to oust President Salva Kiir, and said it has enough evidence to charge them with treason.
The government said the four will not be freed until they have been through the full legal process. It was unclear when that process would begin.
Chief government negotiator Nhial Deng Nhial blamed the opposition for not honoring the cessation of hostilities agreement reached last month.
"We had expressed our concern about the inability of the other party to control its forces and make them abide by the cessation of hostilities agreement," he said.
Fighting has continued in parts of South Sudan, with reports coming in as recently as Tuesday of clashes in oil-producing Unity state and of anti-government forces still in control of parts of Upper Nile state.
The second round of talks is expected to begin in earnest on Wednesday.
Lucy Poni contributed to this story from Nairobi.