Nearly seven million people from South Sudan need emergency aid such as food, water and basic medicines due to a protracted civil war in the country.
The United Nations said this on Thursday and appealed to international donors for $3.2 billion.
The violence in the world's youngest nation is in its fifth year, and has resulted in the deaths of tens of thousands of people. One in three South Sudanese have fled their homes - almost 90 per cent of them are women and children.
"The price of $3.2 billion seems very high. But what the world spends on war is about $15 trillion. $3.2 billion is a big figure, but when you compare it with what is spent on what caused this crisis, it is not too much," Filippo Grandi, UN High Commissioner for Refugees (UNHCR) told a press conference.
"It is the price which we must pay to help people remain alive - and to continue to have opportunities and hope for the future."
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Grandi made the remarks after visiting the Kakuma refugee camp in northern Kenya, where thousands of South Sudanese have sought safety, with more people arriving daily.
South Sudan plunged into civil war in late 2013 after clashes between troops loyal to former vice president Riek Machar and President Salva Kiir.
Efforts to find peace between warring factions have failed. A truce negotiated in December was violated within hours.
The UN says the number of South Sudanese refugees could exceed three million by the end of the year - making it Africa's largest refugee crisis since Rwanda's genocide in 1994.
Almost 2.5 million people have been forced to seek refuge in Uganda, Kenya, Sudan, Ethiopia, the Democratic Republic of Congo and the Central African Republic. The UN says a further two million are displaced inside the country.
Children are at risk of malnutrition; many are unable to attend school and have been recruited by armed factions. Women have reported being raped after their husbands were killed.
Yet despite this, donor funding is low.
Last year, for example, the UNHCR said it received only a third of the funds it needed to support refugees.
"It is impossible to overstate the suffering faced by the people of South Sudan. These funds are not needed by the end of the year, they are needed now," said Mark Lowcock, head of U.N.'s Office for the Coordination of Humanitarian Affairs