South Sudan
A girl walks through mud in the internally displaced persons camp inside the United Nations base in MalakalReuters

The scale of humanitarian operations in South Sudan is the largest in any single country and the world's youngest nation is on the brink of a "catastrophe", a top United Nations official has warned.

Ahead of a visit by UN Security Council members to Africa next week, the deputy peacekeeping chief Edmond Mulet said that almost four million people are at risk of starvation amid growing concerns of famine.

Mulet warned council members that militia violence in South Sudan, the world's youngest nation, which became independent in July 2011, has caused widespread displacement of more than a million people. Around 500,000 more have fled across borders.

"After three years of independence, South Sudan is on the brink of a humanitarian catastrophe and a protracted internal conflict," Mulet said.

"This is a man-made crisis, and those responsible for it have been slow in resolving it."

The cholera epidemic is worsening and over 5,000 cases of cholera have been reported in the country, resulting in nearly 100 deaths, Mulet added. An outbreak in Wau Shilluk in Upper Nile State has claimed about 20 lives alone.

An estimated 10,000 people have been killed since fighting erupted in December 2013, when a political power struggle broke out between President Kiir and his ex-deputy Riek Machar, as the president accused Mr Machar and ten others of attempting a coup d'état.

The conflict has led to inter-ethnic fighting between Kiir's Dinka and Machar's Nuer. Although Kiir and Machar agreed to a ceasefire in May, but little progress has been made so far.

According to Mulet, the UN peacekeeping operation in South Sudan was sheltering nearly 100,000 civilians at its bases.

"With the prolonged presence of this considerable number of people at the facilities which were not built for such a purpose, conditions have become extremely challenging," he said.

The Security Council has almost doubled the mandated number of peacekeepers at the end of December to 1,323 police officers and around 12,500 troops.

As of Monday, Mulet said there were around 1,000 police officers and 10,500 troops.

Joseph Moum Malok, South Sudan's envoy to the UN, said his government was committed to reaching a "final settlement for the conflict through negotiation", according to Al Jazeera.

He added that it has been "forced to react in self-defence to protect its citizens".

On Monday, peace talks between South Sudan's government and rebels in Ethiopia were restarted with the aim of creating a transitional government.