Cholera has broken out in the Juba, the capital of South Sudan where months of civil war has left thousands homeless and disrupted food supplies and health services, according to the World Health Organization.
The confirmed cases come as donors prepare to meet in Oslo to discuss the dire food security situation in the world's newest country.
Cholera is spread through contaminated water and unclean food, so the hundreds of thousands of people internally displaced due to the political crisis are at risk in overcrowded settlement areas. Oxfam's South Sudan director Cecilia Milan said:
"The confirmation of 138 cholera cases in Juba is a stark reminder of the multitude of risks the citizens of this country have been forced to endure since conflict broke out in December 2013.
"There is no question - the international community must act now to prevent a rapidly escalating food crisis - and now potentially a public health emergency - In South Sudan."
The UK will give £60 million to aid agencies working in South Sudan, in an attempt to meet the the "dire" needs of the civilian population fleeing the deadly civil conflict in the newly formed state.
Hundreds of thousands of people have been forced to flee their farms and homes to neighbouring regions and refugee camps, and the situation is expected to deteriorate in the coming months as the rainy season starts. South Sudan's chronic lack of roads and infrastructure will hamper relief efforts.
Development Minister Lynne Featherstone said:
"The situation is dire, getting worse, and 7.3 million people are going to be in need"
None of the money is going through the South Sudan government, instead it will go directly to aid agencies or the UN.
Millions of people in South Sudan are in urgent need of humanitarian assistance to prevent famine, the UN said, as donors prepare to meet in Oslo today to discuss the deteriorating crisis.
The UN said the situation is likely to deteriorate over the coming months.
- Currently, 6.9 million people are acutely food insecure
- 3.7 million people require urgent humanitarian assistance
- From June to August this number will increase to 7.3 million
- Populations face the risk of famine unless humanitarian aid is delivered
Delivering aid to the areas afflicted is complicated and time consuming due to the ongoing affects of the conflict and resulting displacement, and chronic lack of resources and infrastructure.
Norway will host a humanitarian conference for South Sudan in Oslo today, as the UN warned urgent action is needed for millions displaced from their homes who are now facing acute food insecurity.
The meeting comes after the president of South Sudan told the BBC he needed humanitarian assistance.
Salva Kiir said his country faces one of its worst famines unless the current conflict ends. He said it was essential that humanitarian agencies were allowed to work.
The South Sudanese President Salva Kiir and rebel commander Riek Machar have agreed to a ceasefire deal after coming under growing international pressure to end ethnic fighting that has raised fears of genocide in the African nation.
The deal by the two men in Ethiopia was the first time they had met since violence erupted in mid-December following a long power struggle.
Kiir and Machar shook hands and prayed together during the ceremony.
The men also agreed that a transitional government offered the "best chance" to take the country towards elections next year.
The US is planning on imposing sanctions on individuals on both sides of the South Sudan conflict, diplomatic sources have told Reuters.
The sources, who spoke to Reuters on condition of anonymity, said that the sanctions would involve a ban on travel to the United States and the freezing of any assets under U.S. authority. People on both the rebel and government sides will be targeted, the sources added, without disclosing names.
News of an imminent US move came as Secretary of State John Kerry threatened sanctions against South Sudan rebel leader Riek Machar if he spurned peace negotiations, while government forces battled for control of the northern oil town of Bentiu.
At least 200 South Sudanese civilians have drowned in a ferry accident on the White Nile river while fleeing fighting in the city of Malakal, Agence France-Presse have reported.
An army spokesman reportedly said the boat was "overloaded" and was carrying "between 200 to 300 people, including women and children".
Heavy fighting was reported in Malakal, state capital of oil-producing Upper Nile state, as rebel forces staged a fresh attack to seize the town.
According to the United Nations, some 400,000 civilians have fled their homes over the past month.
The fighting is between South Sudan's President Salva Kiir and his former deputy Riek Machar.
South Sudanese rebels and a government delegation have started peace talks to try to end fighting that has left the world's newest state on the brink of civil war.
The talks in neighbouring Ethiopia will focus on brokering a ceasefire to halt three weeks of violence that has killed at least 1,000 people and driven 200,000 from their homes.
"We have begun our meeting on the cessation of hostilities," a member of the government delegation told Reuters. The fighting, often along ethnic faultlines, has pitted President Salva Kiir's SPLA government forces against rebels loyal to former vice president Riek Machar.
South Sudanese rebels loyal to former Vice President Riek Machar have seized control of Bor, the capital of restive Jonglei state, the town's Mayor has said.
Nhial Majak Nhial told Reuters that government troops loyal to President Salva Kiir had made a "tactical withdrawal" to Malual Chaat army barracks, some two miles south of the town yesterday.
The East African regional bloc IGAD says that the South Sudan government and rebels have agreed on a cessation of hostilities, according to Reuters.