South Sudan rebel leader Riek Machar was sworn in as first vice president on Saturday, formally rejoining the government in the latest bid to bring peace to a nation ravaged by war. President Salva Kiir hailed the "official ending of war" and said peace was now "irreversible" as the new unity government was formed after more than a year of delays and bickering over crucial issues. It is the third time that bitter foes Machar and Kiir will attempt to rule together and the pair have many differences yet to iron out as they form a government that is a cornerstone of a September 2018 peace deal.

"For the people of South Sudan, I want to assure you that we will work together to end your suffering," Machar said after taking the oath and embracing Kiir.

The rebel leader returns as first vice president in a transition government which will serve for 36 months. Four other vice presidents from the current regime and other opposition groups will also form part of a bloated government of 35 ministers, in addition to 550 lawmakers.

The rivals started out as president and deputy at independence in 2011 but Kiir sacked Machar in 2013 and later accused him of attempting a coup against him, sparking a war characterised by ethnic bloodshed between Kiir's Dinka and Machar's Nuer communities. "We must forgive one another and reconcile. I also appeal to the people of Dinka and Nuer to forgive one another," said Kiir.