(AFP) - The United Nations said Monday that $1.4 billion (1.3 billion euros) was needed this year alone to help the nearly two million people who have fled war and famine in South Sudan.

The UNHCR refugee agency and the World Food Programme presented an updated response plan to the crisis in appealing for nearly double the $781 million they had previously said they needed.

"Bitter conflict and deteriorating humanitarian conditions in South Sudan are driving people from their homes in record numbers," UNHCR chief Filippo Grandi said in a statement.

South Sudan, the world's youngest nation, fell into a brutal civil war in December 2013, just two years after it spilt from the north.

Tens of thousands of people have been killed in the country since then, with some 1.8 million forced to flee the country, including about one million children, to seek refuge in Uganda, Sudan, Ethiopia, Kenya, the Democratic Republic of Congo and the Central African Republic.

Another two million have been displaced inside the country, but they are not covered by Monday's appeal.

The country has declared famine in some areas and has warned that a million people are on the brink of starvation.

"The suffering of the South Sudanese people is just unimaginable," WFP chief David Beasley said in a statement, saying that many are "close to the abyss."

"Aid workers often cannot reach the most vulnerable hungry people. Many are dying from hunger and disease, many more have fled their homeland for safety abroad," he said.

The UN said people were now fleeing South Sudan at a rate that far exceeded already pessimistic estimates.

"The number of people fleeing to Sudan in March surpassed the expected figure for the entire year," it said, with about 375,000 South Sudanese refugees now in the country.

Ethiopia is hosting the same number, while the situation in Uganda is even more dire, with nearly 900,000 refugees from South Sudan in that country.

Kenya counts about 97,000 South Sudanese refugees, DRCongo has 76,000 and the Central African Republic has 2,200.

Aid agencies are struggling to secure the funds they need to help the refugees, making it difficult to provide food, water, shelter and health services.

So far, only 14 percent of the initial $781 million appeal for 2017 has been provided.

"Our funding situation forced us to cut food rations for many refugees in Uganda," Beasley said, a situation he called "unacceptable".

"These are families like yours and mine, our brothers and sisters, and the world must help them now -- not later," he said.

© Agence France-Presse