The world's newest nation has struggled to find its footing since gaining independence from Sudan in 2011, battling violence, endemic poverty and natural disasters.

The unification of forces loyal to President Salva Kiir and his rival, Vice President Riek Machar, was a key condition of the 2018 peace deal that ended a five-year conflict in which nearly 400,000 people died.

Tens of thousands of former fighters were integrated into the country's army in August last year but none have been deployed until now, with the delays fuelling frustration in the international community.

The first battalion comprising nearly 1,000 soldiers will be deployed to Malakal in northern Upper Nile State, which has received huge numbers of South Sudanese refugees fleeing the conflict in neighbouring Sudan.

At the ceremony on the outskirts of the capital Juba, Santino Wol, the country's chief of defence forces, urged the battalion to remain united, saying: "Be a soldier and don't get involved in politics."

The unity government led by Kiir and Machar has largely failed to meet key provisions of the peace agreement, including drafting a constitution and electoral legislation ahead of polls now set for next year.

Kiir has vowed to hold the country's first ever presidential ballot by December 2024, but UN envoy Nicholas Haysom warned in August that the authorities needed to create a conducive environment to ensure "peaceful, inclusive and credible elections".

"We are going for elections and you are to make sure that peace prevails so that elections can proceed peacefully," Information Minister Michael Makuei told the soldiers on Wednesday.

One of the poorest countries on the planet despite large oil reserves, South Sudan has spent almost half of its life as a nation at war and continues to be roiled by outbreaks of politically motivated ethnic violence.