JUBA - UN Secretary General Ban Ki-moon has reiterated a call for perpetrators of violence in South Sudan to be brought to justice.
"All violence, attacks and human rights abuses must end immediately," Ban's spokesman said in a statement late Saturday.
"The secretary general reminds those responsible that they will be held accountable. He calls on the government and all concerned to ensure the rights and security of civilians are protected," said the statement, issued in New York.
The government on Saturday meanwhile accused sacked former vice president and rebel leader Riek Machar of recruiting up to 25,000 young men of the Nuer tribe in eastern Jonglei state.
But rebel spokesman Moses Ruai Lat denied the allegation, telling AFP that Machar was "not mobilising his tribe", South Sudan's second biggest ethnic group.
Those young people were regular soldiers turning their back on the government and had not been drafted by Machar, he said.
The conflict, fuelled by an old rivalry between President Salva Kiir and Machar, has fanned ethnic differences between Kiir's Dinka group and the Nuer.
The accusations came as East African and Horn of Africa peace brokers set a Tuesday deadline for Kiir and Machar to start face-to-face talks and stop two weeks of fighting that is thought to have left thousands dead in the world's youngest country, which won independence from Sudan in 2011.
The regional grouping the Inter-Governmental Authority on Development is spearheading efforts to end the fierce battles for control over several strategic oil-producing areas notably in the north of South Sudan.
The United Nations, Washington and Beijing are also pressing for talks.
A spokesman for IGAD said President Kiir had on Friday expressed willingness for an "immediate" ceasefire though Machar would not immediately commit to a truce.
The rebel leader said he first wanted a mechanism to monitor any ceasefire as well as the release of all his political allies arrested when trouble first broke out.
Reports of massacres, rapes and murders have emerged in recent days. The United Nations -- whose hard-pressed peacekeepers are to be doubled to more than 12,000 -- said one mass grave had been discovered and large numbers of uncollected bodies were seen outside at least one UN base.
The fighting erupted December 15 after Kiir accused his former vice president of trying to mount a coup. Machar has denied the allegation and retorted that Kiir was trying to eliminate his rivals.
Rebels quickly took control of a few key regional cities including Bentiu, in the northern oil-producing state of Unity, as well as Bor which was recaptured by the army on Tuesday.
The death toll nationwide is said to be several thousand. The United Nations has said more than 120,000 residents have been displaced since the conflict started.