Nicholas Haysom, the head of Unmiss, told reporters in the capital, Juba, that South Sudan "will unravel as a result of what is happening in Sudan" noting that the war's negative effects would be felt beyond the country.

He said a disruption of South Sudan's oil pipeline to Sudan - through which the landlocked country exports all its crude oil - would have an immediate impact.

He said South Sudan and its citizens' capacity "to simply get by" would be affected "because 90% of the services and salaries all come from the oil money".

"So in that regard, we would certainly want to argue – loudly, strongly, repeatedly – that the war has to come to an end,” Mr Haysom added.

The fighting between the Sudan army and the paramilitary Rapid Support Forces (RSF), now on its sixth week, has displaced nearly one million people, according to the UN.

The number of South Sudanese returnees who have fled the conflict and returned home has exceeded 70,000, according to Unmiss.