Around 2.7 million people in South Sudan will require food aid from next year with crop failures and violence hitting Africa's newest nation hard, the United Nations said on Thursday.

South Sudan won its independence from Sudan in July but the new nation has been struggling to build up state institutions, end tribal and rebel violence and overcome an economic crisis.

Landlocked South Sudan imports much of its food needs from Sudan but border trade has been disrupted by armed clashes.

More than 80,000 people have fled to South Sudan from northern border states where Khartoum's army has been fighting insurgents for months.

Erratic rains have caused food prices to spiral upwards in recent months and various armed conflicts have worsened the crisis, the U.N. World Food Programme (WFP) said in a statement.

A gathering storm of hunger is approaching South Sudan, caused by crop failure and market disruption, WFP country director Chris Nikoi said in a statement.

Resources are being stretched further by people displaced by violence and an influx of 350,000 South Sudanese returning home following independence in July, according to the WFP.

WFP and the U.N. Food and Agriculture Organisation estimate that the young nation will have a shortfall of 400,000 metric tons of food in 2012. Inflation climbed to 78.8 percent in November in the country of 8.3 million people.

Food prices have already doubled or tripled in some areas, leaving hundreds of thousands of children vulnerable to malnutrition at a key developmental stage of their young lives, Nikoi said.

Relations between Juba and Khartoum have soured in recent weeks as talks over post-independence issues such as oil, debt, arrears, disputed areas and transitional financial assistance have broken down.

Sudan and South Sudan regularly trade accusations -- and denials -- of supporting insurgencies in each other's country, although direct combat between the two armies broke out in a border area claimed by both sides.

Conflict, growing insecurity -- including the laying of landmines by rebel groups -- and poor road infrastructure are hindering access for humanitarian operations, WFP added.

(Reporting by Hereward Holland; Editing by Ulf Laessing and Mark Heinrich)