A deal signed by South Sudan's president aimed at ending 20 months of civil war was given a cautious welcome Thursday, with both sides in the conflict urged to show good faith.

At least seven ceasefires have already been agreed and then shattered within days or even hours since war began in December 2013.

African Union Commission chief Nkosazana Dlamini-Zuma said Thursday the deal was "a critical step in the efforts aimed at ending the conflict" but said the agreement must be implemented.

"Seize this unique opportunity to open a new chapter," she said, calling on all sides to "scrupulously abide by its terms and faithfully implement its provisions."

Serious concerns remain. President Salva Kiir signed the peace accord on Wednesday at a ceremony in Juba, but he annexed a list of reservations that would have to be addressed for the agreement to take hold.

Both sides traded blame Wednesday for attacking each other. Under the deal, a permanent ceasefire must come into force by nightfall on Saturday.

The UN Security Council has given Kiir until September 1 to get fully behind the agreement or face possible sanctions, and the United States has circulated a draft resolution that would impose an arms embargo and targeted sanctions on those who undermine peace efforts.

Key aid agencies, that are struggling to stem a humanitarian crisis in the devastated nation, said in a joint statement that even if implemented the deal was "only the beginning of a long, hard journey towards peace and reconciliation."

Tens of thousands of people are thought to have died in a war marked by ethnic killings, gangs rapes and child soldier recruitment.

"The value of the peace deal will only be seen on how it is implemented on the ground," the International Rescue Committee (IRC) said.

- 'More than words' -

"The people of South Sudan need more than words," said John Hoare from CARE aid agency. "They need real commitment from their leaders to ensure that this is a lasting peace, that the violence has ended and the reconciliation process can begin."

The deal was brokered by the regional eight-nation IGAD bloc, along with the UN, the African Union, China, Britain, Norway and the United States.

The conflict has been characterised by ethnic massacres and rape.

"Much more needs to be done to ensure lasting peace and stability," said Oxfam chief in South Sudan Zlatko Gegic.

"With millions of people hungry, it is crucial that all warring parties respect the agreement, stop fighting immediately and allow life-saving aid to reach people where they are."

Before signing, Kiir himself warned of the risk of failure, saying there were "so many things we have to reject" in the deal, and that "such reservations, if ignored, would not be in the interests of just and lasting peace."

He also called on regional leaders at the signing ceremony -- including Ethiopia, Kenya, and Uganda -- to support the deal.

"Stand with us in the implementation," he said. "Otherwise we may spoil it, if it is left to us."

South Sudan peace deal: key points to end war
Juba (AFP) Aug 26, 2015 - South Sudanese President Salva Kiir is expected to sign a peace deal Wednesday, aimed at ending 20 months of civil war.

At least seven ceasefire deals have been agreed and then shattered within days - if not hours - in the world's newest country, which broke away from Sudan in 2011.

The latest proposed deal, already signed by rebel chief Riek Machar, sets out clear steps towards power sharing, with fixed timeframes for implementation.

The deal is backed by the regional eight-nation bloc IGAD, the Intergovernmental Authority on Development, as well as the United Nations, African Union, China, Britain, Norway and the United States.

South Sudan's government has expressed "reservations" about the deal, and it remains unclear if Kiir will sign all its clauses.

Here are the key points of the 72-page agreement.

- Ceasefire -

Fighting must end immediately, with a "permanent ceasefire" beginning 72 hours after the deal is signed.

Troops on either side have 30 days to gather for "separation, assembly and cantonment" - or confinement to barracks, with their weapons kept in storage - with a security review required before an eventual merger of the two forces.

- Foreign forces out -

All foreign forces embroiled in the war - mostly Ugandan troops backing Kiir - must leave within 45 days.

Foreign militias, including rebels from neighbouring Sudan's Darfur and Nuba mountain regions, must also be disarmed and sent home.

No troops are allowed within a 25-kilometre (15-mile) radius of the capital Juba. Only presidential guard members, police and guards protecting infrastructure can remain in the city.

Child soldiers and prisoners of war must be released, and free access given to aid workers.

- First vice-president -

The deal gives rebels the post of "first vice president", alongside the current vice president. That means Machar would likely regain the post he occupied before being sacked by Kiir in July 2013, six months before the war began.

Signatories also take responsibility for the war, "apologising unconditionally" for the tens of thousands killed in a conflict marked by widespread atrocities on both sides.

- Transitional government -

A "transitional government of national unity" will take office 90 days after the signing of the deal and govern for 30 months.

Elections must be held 60 days before the end of the transitional government's mandate - meaning that if Kiir signs now, polls would be slated for early 2018.

At a national level, the government gets 53 percent of ministerial posts and the rebels 33 percent, with the remaining seats for other parties.

In seven of the 10 states, the government will get 85 percent of ministerial posts. But in the battleground states of Jonglei, Unity, and Upper Nile, the government gets 46 percent and the rebels 40 percent of posts.

In Unity and Upper Nile states, the main oil regions which have been among the areas hardest hit by the war, the rebels also get to select the powerful post of governor.

- War crimes court -

A Commission for Truth, Reconciliation and Healing will be set up to investigate "all aspects of human rights violations."

A "hybrid court", set up in collaboration with the African Union, will try crimes, including possible genocide, crimes against humanity and war crimes.

Those indicted cannot be part of the transitional government.

"No one shall be exempted from criminal responsibility on account of their official capacity as a government official, an elected official or claiming the defence of superior orders," the deal says.