South Sudan peace deal hailed, but will it hold?

The truce signed by President Salva Kiir and former Vice-President Riek Machar late on Friday in neighbouring Ethiopia calls for a cessation of hostilities within 24 hours and unhindered humanitarian access.

Though it the second peace deal of the nearly five-month conflict, the two leaders did not attend talks that forged the first ceasefire in January. This time they met and shook hands, a hopeful sign one week after US secretary of state John Kerry met with Kiir in South Sudan's capital and spoke to Machar by phone. Only days later, UN secretary general Ban Ki-moon flew in, adding to the pressure.

The fighting, which has often pitted Kiir's ethnic Dinka against Machar's ethnic Nuer, has killed thousands of people, often in what a new UN report this week said were gross violations of human rights "on a massive scale". More than 1.3 million people have fled their homes, and aid officials fear that mass hunger will set in later this year.

"Big news from Addis," Toby Lanzer, the top UN aid official in South Sudan said on Twitter on Saturday. "Calling on both parties to facilitate deliveries of emergency relief to people in need now: open roads for truck convoys & rivers for barges."

Asked by The Associated Press if there is any evidence that the parties will open up aid access, Lanzer replied: "It's a better result than many would have expected."

Among others voicing caution was John Prendergast, the co-founder of the Washington-based Enough Project, which does advocacy work in eastern and central Africa.

"We will know very quickly whether the parties are serious, as they are right now poised to attack each other in a number of volatile locations on the front lines of the war. It is crucial to deploy the regional civilian protection force and cease-fire monitors to ensure some measure of compliance. If this falls apart, the fighting will enter an even bloodier phase as the stakes continue to increase" Prendergast said.

Asked if Kiir's military would hold up its side of the ceasefire deal, the South Sudan military spokesman, Colonel Philip Aguer, responded "definitely". He said the new deal has a better chance of holding since Machar signed it himself. But he acknowledged violence could return if rebels, perhaps if there are some Machar can't control, continue attacks.

"There can still be a problem if they don't listen and don't stop attacking, then definitely the government forces will have to defend themselves," Aguer said.

A statement on Friday by the spokesman for Ban, the UN chief, demanded that both sides "immediately translate these commitments into action on the ground".

International pressure had been growing for at least a brief ceasefire to alleviate hunger fears. Lanzer included in his tweet the phrase "May Month of Tranquillity" as a Twitter hashtag. Aid officials say if residents don't immediately return home and plant crops before seasonal rains arrive in force in June, then the country risks mass hunger and perhaps famine.

Kiir and Machar agreed to establish a "transitional government of national unity" that will lead to new elections, said a statement by the regional bloc IGAD, which brokered the talks. The two also agreed to meet again in a month, while IGAD leads talks on the terms of the transition.

The UN security council recently discussed sanctions, an arms embargo and a referral of the South Sudan situation to the International Criminal Court as ways to apply pressure.

South Sudan is a largely Christian and animist nation that broke off from the Muslim-dominated Sudan after a 2011 referendum. The fighting is an embarrassment to the US, which has provided hundreds of millions of dollars in aid and has been its strongest international champion.