Kiir said he was deeply touched and had "trembled" in April when Pope Francis kneeled to kiss his feet at a Vatican retreat with his rival, adding that this had laid a heavy responsibility on his shoulders.

"I have completely forgiven him (Machar) and all I ask from him is to become a peace partner, for he is no longer my opponent," Kiir told the opening of a new session of parliament.

"In the spirit of (the peace deal) and our experience in Rome, I once again extend my invitation to Dr. Riek Machar to return home."

The two main actors in a devastating conflict that is now in its sixth year, signed a peace deal in September 2018 which was meant to culminate in a power-sharing government on May 12.

However numerous issues such as the creation of a unified army have yet to be dealt with and the formation of the government has been delayed another six months.

Machar is also concerned about his personal security should he return to the capital, after fleeing on foot under a hail of gunfire when a previous peace deal collapsed in July 2016.

He is currently living in Khartoum.

Kiir's political will to implement the deal has been in question, particularly after it emerged he had hired a US lobby group to block the creation of a war crimes court that is part of the agreement.

The president nonetheless insisted he was committed to the deal.

- Country at a crossroads -

"Our country stands at a crossroad, to embrace and consolidate peace or to slide back to war. I stand for peace and stability and I completely reject war.

"My government shall therefore spend all resources at its disposal for the purposes of consolidating peace and stability in our moral and religious duty to bring peace to our people."

Kiir also reflected on his time with the pope, who stunned the world by kneeling to kiss the feet of two men accused of responsibility for heinous war crimes.

"To be honest, I was shocked and trembled, but I also knew deep down my heart that his Holiness did this to show Christ's humility.

"Pope Francis' act of humility is both a blessing and a curse on all of us. A blessing, if we heed to his call for peace and a curse if we play games with the lives of our people."

South Sudan's war has left 380,000 people dead and forced more than four million South Sudanese -- almost a third of the population -- to flee their homes. Numerous attempts to restore peace have failed.