- By Joel Barnett
Famine has been declared in two regions of South Sudan following a three-year civil war and a severely entrenched economic crisis.
Some 100,000 people in Unity state are experiencing famine and it is feared it will spread further in the coming months.
An estimated one million South Sudanese are on the brink of starvation, according to a report by South Sudan's government and three UN agencies.
However even as the announcement was declared, UN officials claimed President Salva Kiir's government blocked food aid to some areas.
- When does a food crisis become a famine?
According to the UN, a famine can only be declared when certain measures of death, malnutrition and hunger are met.
Due to its level of severity, a famine can only be classified when at least 20% of households in an area face extreme food shortages and a limited ability to cope.
The area must also have acute malnutrition rates that exceed 30%, and a death toll in excess of two persons per day, per 10,000 people.
- UN: "Our worst fears have been realised"
Serge Tissot, head of the Food and Agriculture Organization in South Sudan, said: "Our worst fears have been realised."
Speaking to ITV News, he said the civil war had disrupted the otherwise fertile country as farmers have fled their lands to escape the violence.
Mr Tissot warned that farmers must be able to return to their lands soon, otherwise "we will face a major famine crisis in the coming months."
He said: "It's not normal to have farmers in refugee camps outside the country. There is no future of the country if the farmers are not on their land.
"The target is to restore the livelihood of the people. People need to grow their own food. They need to survive by themselves, that is the target.
"We can [only] start to build the development of the country when [the farmers are] back."
- "Children stand a very high chance of dying without help"
Mr Tissot added that some 5.5 million - roughly 50% of South Sudan's population - are expected to be severely food insecure and at risk of dying in the next three months.
Among them are an estimated 250,000 children who are severely malnourished.
Unicef spokesperson Jeremy Hopkins said children in the region "stand a very high risk of dying" if the organisation remains unable to gain safe access to the affected areas.
He told ITV News: "We need to have safe and secure access to the affected population.
"If we get that access we are able to provide the lifesaving support that we know how to provide to children - who stand a very high risk of dying if we don't manage to reach them.
"Were we to have safe access to the population affected, we will be able to avert the very worst that pre-famine levels present."
Michael Keizer, deputy head of mission for Medecins Sans Frontieres in South Sudan, said the organisation has mounted "a nutritional response to the elevated levels of malnutrition".
Speaking to ITV News, Mr Keizer said: "The conflict in the country has ensured a lot of people are on the move.
"They have a lack of access to [medical] services. There is quite a lot of issues because of the conflict.
"We see people in our clinics who are fleeing from the violence, and as a result have many different health problems including malnutrition.
"We would like to see the parties in the conflict respect the civilian population and their rights."
Priti Patel, the UK's international development secretary, vowed that Britain "will not look the other way" and highlighted British efforts to support South Sudan's population.
"This is an urgent and severe crisis, with almost half the population in desperate need," Ms Patel said in a statement.
"The UK will not look the other way while people of South Sudan suffer. The government of South Sudan must put an end to ethnic violence, allow humanitarian access and deliver long-lasting peace.
"The international community now needs to step up alongside Britain to stop famine spreading and help support stability in South Sudan and the region, which is firmly in all our interests."
Tens of thousands of people have died and more than three million people displaced since civil war broke out across the country in December 2013.
The UN has previously warned South Sudan stands on the brink of genocide.