President Uhuru Kenyatta on Thursday accused the United Nations of "scapegoating" Kenyan soldiers for the failings of the UN peacekeeping mission in South Sudan.

He followed up on Wednesday's announcement, when Kenya, angered at the dismissal of the Kenyan head of the force, declared it would withdraw its soldiers from South Sudan and disengage from its mediation role in the peace process.

"We know that the people of this region want peace in South Sudan. But we also know that peace will not come to South Sudan by blaming a Kenyan commander for the wider failings of the mission to South Sudan," Kenyatta said.

Lieutenant-General Johnson Mogoa Kimani Ondieki, was sacked on Tuesday as head of the UNMISS force after a UN probe found he had presided over a "chaotic and ineffective response" to fighting in the South Sudan capital in July.

The violence saw soldiers kill civilians, loot warehouses and rape women, including foreign aid workers.

Ondieki is the only official to be held to account so far.

Kenya, which provides 1,050 of the 13,500 troops deployed as part of the UN Mission in South Sudan (UNMISS), plans to begin the withdrawal immediately.

"We will no longer contribute to a mission that has failed to meet its mandate, and which has now resorted to scapegoating Kenyans," Kenyatta said.

"Serving does not come at the expense of the country's dignity," he added.

In Wednesday's angrily-worded statement, Kenya's foreign ministry announced the withdrawal of its existing peacekeepers.

It added it would no longer contribute to a proposed 4,000-strong "regional protection force" intended to bolster the UN mission and would also "disengage" from the peace process that has so far failed to end fighting since December 2013.

A UN official in South Sudan said discussions would begin on the troop withdrawal.

"This is the prerogative of the Kenyan government and we respect it," the official said.

"We will now consult with the Kenyan government regarding the modalities of withdrawal of its contingent."