Conflict, population displacement and high food prices mean millions of people in South Sudan face hunger this year, two U.N. food agencies said on Wednesday.

The number of people with insecure food supplies has risen to 4.7 million in 2012 from 3.3 million in 2011, a report by the Food and Agriculture Organisation (FAO) and World Food Programme (WFP) said.

Of those, about one million people are severely food insecure, and that number could double if fighting continues and prices keep rising, the report said.

This is a rapidly approaching crisis that the world cannot afford to ignore, said WFP country director Chris Nikoi.

South Sudan became independent in July under a 2005 peace agreement with its former civil war foe, Khartoum, but has been struggling to tackle economic turmoil and contain tribal and rebel violence which has killed thousands.

National cereal production in 2011 was 25 percent lower than average for the last five years and the cereal deficit for 2012 is estimated at almost half the country's total consumption needs for the year, the report found.

There is also significantly increased demand for food from South Sudanese returning from the north and people displaced by conflict, the agencies said.

The closure of border crossings linking South Sudan to Sudan has disrupted the supply of commodities. High fuel costs and the depreciation of the South Sudanese pound have also contributed to steep food inflation.

The report follows a FAO-WFP mission to South Sudan in October and November 2011.

WFP is aiming to reach 2.7 million people with food aid, but estimates its funding shortfall at $160 million (101 million pounds).

FAO wants to provide agricultural support to revive production for the next crop season that starts in April, and is seeking $23 million (14 million pounds) in donor support.

(Writing by Catherine Hornby; Editing by Janet Lawrence)