South Sudan president blasts UN for wanting 'parallel' government

South Sudan's President Salva Kiir has lashed out at the United Nations following heavy criticism including accusations of atrocities in the conflict gripping the young nation.

Kiir's comments come after UN chief Ban Ki-moon expressed alarm at reports that senior government figures and troops threatened UN staff when they tried to enter a peacekeepers' compound to which thousands of civilians had fled.

"We did not know that when the UNMISS was brought to South Sudan they were brought as a parallel government... but they have showed it very clearly in this conflict," Kiir said in a speech on Monday, referring to the UN Mission in South Sudan.

"They fall short of naming the chief of UNMISS as the co-president of the Republic of South Sudan," he added.

"They just fall short of that, and if that is the position of Ban Ki-moon he should make it clear that he wants the UN to take over South Sudan."

Ban had said that the threats were "just one of a growing number of violations" of the UN accord with the South Sudan government "making it increasingly difficult for UNMISS to implement its mandate and dangerous for United Nations staff working in South Sudan".

Last week, the United Nations' top human rights envoy, Ivan Simonovic, detailed reports of mass killings, sexual violence and widespread destruction, with atrocities reported on both sides.

Thousands have been killed and half a million civilians have been forced to flee the fighting that broke out last month.

Over 67,000 are sheltering inside UN bases.