Representatives from South Sudan's government and the opposition agreed on a ceasefire deal on Thursday. The agreement was signed in the Ethiopian capital, Addis Ababa, where the two sides have been working to negotiate an end the deadly conflict for several weeks.

The deal on Thursday stipulated that fighting would be halted within 24 hours. Initial reports did not provide further details on the terms of the peace deal, which the East African bloc Intergovernmental Authority on Development (IGAD) helped broker.

"Despite the signature on the cessation of hostilities, we have no illusions that the implementation will be easy," government chief negotiator Nhial Deng said, according to DPA news agency.

IGAD's chief mediator, Seyoum Mesfin, echoed this sentiment.

"I believe that the postwar challenges will be greater than the war itself. The process will be...unpredictable and delicate," said Mesfin.

Clashes erupted in Africa's youngest country on December 15 when Vice President Riek Machar attempted to stage a coup against President Salva Kiir's government. The former vice president denied responsibility. The duo are long-time rivals, with President Kiir having ousted ex-Vice President Machar from his post in July. The two are also split along ethnic lines. Kiir belongs to the Dinka group, while Machar is Nuer.

Thousands have died in the subsequent fighting and more than half a million have been forced to flee their homes in that time, according to the latest figures from the United Nations.

UN: 'Mass atrocities' in South Sudan

On Friday, the UN's top humanitarian official announced evidence of mass atrocities by both sides of the conflict following a visit to the country.

Assistant secretary-general for human rights, Ivan Simonovic, said child soldiers were increasingly being used. He also cited reports of mass killings, extrajudicial executions, arbitrary detentions and sexual violence.

He added that the unrest could now be classified as an "internal armed conflict," meaning that war crimes law applies. He called for a fact-finding commission to investigate atrocities and hold those responsible accountable.

kms/av (AP, AFP, Reuters, dpa)