South Sudan main rivals have signed the long-awaited final peace agreement to end the five-year war in the country.

President Salva Kiir and opposition leader Riek Machar late Wednesday shook hands after signing the deal in neighbouring Ethiopian capital Addis Ababa.

The two re-committed themselves to implement the deal in letter and spirit in a ceremony attended by Igad heads of state and government.

"The eyes of the world are upon us as the South Sudan leaders commit today to press for reconciliation and lasting peace in their country," Ethiopian Prime Minister Ahmed Abiy said in a statement.

However, another rebel faction, the National Salvation Front (NAS) led by former army deputy chief, General Thomas Cirillo, rejected the agreement, saying it was fake.

Federal system

NAS spokesperson Suba Samuel said the pact fails to address the root causes of the war and only focuses on power sharing.

He also warned that the war would continue in the country if their demand for federal system of governance was not accepted.

"The calamity in South Sudan will continue if the government in Juba does not heed to the demand for a just peace," Mr Suba said.

International experts have expressed doubts over the credibility of the accord.

Return to war

Mr John Prendergast, the founding director of Enough Project, said the deal contained significant flaws such as corruption.

"Today's peace lacks meaningful checks and balances on a presidency that already wields immense powers, which are primarily used to loot the country's resources and deploy extreme violence against opponents," he said.

Another commentator, Mr Brian Adeba, said the peace deal was a division of the spoils between the rival factions with biggest guns.

"The signed agreement reinforces the status quo and increases the odds of a full-fledged return to war, in its failure to address Sate capture by these politicians or reformed in hijacked institutions," he said.

Humanitarian crises

This is the second peace agreement mediated by Igad following round of talks in Khartoum that started in June that led to the signing of a new ceasefire after a face-to-face meeting between President Kiir and Dr Machar.

The first deal was signed in 2015, but collapsed in July 2016, resulting to an implosion in Juba and Dr Machar fleeing to South Africa.

South Sudan plunged into war in December 2013 following a quarrel between President Kiir and Dr Machar over political reforms.

The war claimed many lives and caused one of the worst humanitarian crises in the continent since the 1994 Rwanda genocide , according to the UN.