Some 3.7 million people are food insecure in South Sudan and up to 7 million - 85 percent of the population - are at risk, the U.N. Food and Agriculture Organization (FAO) warned on Wednesday.
The FAO has appealed for $77 million to help those affected, bringing to a total of $1.29 billion the sum needed to meet the country's urgent humanitarian needs in the first half of 2014.
Fighting between South Sudan's army and rebels led by former Vice President Riek Machar, which erupted in mid-December, brought the world's newest nation to the brink of civil war and caused a humanitarian crisis. The two sides signed a ceasefire on Jan. 23 but sporadic clashes have continued.
"South Sudan was already the scene of one of the world's largest humanitarian operations before the fighting began, and the situation is now deteriorating rapidly," Sue Lautze, FAO Head of Office in South Sudan, said in a press release.
Displacement has disrupted the crop cycle and the FAO said that food insecurity would be even worse if farmers missed the main planting season in March.
"Markets have collapsed, infrastructure is damaged, foreign traders have fled, commodity supply corridors have been disrupted by violence, and rural populations are unable to bring their crops, livestock and fish to market for sale", said Lautze.
South Sudan imports most of its staple foods from neighbouring countries, and domestic and cross-border trade in Jonglei, Unity and Upper Nile states has been halted by the fighting.
The U.N. has said that as many as one million people have been displaced across the country, and aid agencies say insecurity is hampering their operations.
Many of the displaced who have sought shelter along rivers may have to move again because the approaching rainy season will raise water levels.