By Katy Migiro

NAIROBI, April 5 (Thomson Reuters Foundation) - A record 5.8 million people in South Sudan or half its population do not know where their next meal will come from as conflict and poor rains have increased cereal prices by nearly five-fold in a year, the United Nations said on Tuesday.

Hunger in South Sudan has worsened significantly over the last year to its highest harvest time level since systematic data collection began in 2010, the U.N.'s Food and Agriculture Organization and World Food Programme (WFP) said.

"South Sudan is facing a deadly blend of conflict, economic hardship and poor rains," WFP's country director Joyce Luma said in a statement.

"They are worsening a hunger gap that we fear will force more people to go hungry and increase malnutrition."

The world's youngest nation, which ceded from Sudan in 2011 after a lengthy war, needs peace to feed its people, she said.

The proportion of people who are moderately or severely food insecure, which means they do not have enough to eat or cannot afford the food that is available, have risen to a high of 49 percent from 38 percent over the past year, the agencies said.

A political dispute between President Salva Kiir and his former deputy, Riek Machar, sparked conflict in 2013, forcing more than two million people from their homes. Tens of thousands were killed in ethnic clashes.

The two leaders signed a preliminary peace deal in August and Kiir re-appointed Machar as vice president in February.

Despite this, conflict has continued, paralysing markets.

Violence broke out this year in the breadbasket regions of Bahr el-Ghazal in the west and Equatoria in the south, which were previously largely unaffected by the war.

Numerous roadblocks have sprung up and truck drivers taking food to market are often asked to pay "exorbitant ad hoc taxes", the agencies said.

They said the 2015 cereal harvest is down 9 percent on 2014, largely due to poor rains, while higher transport costs and a sharp fall in the South Sudanese currency have also pushed cereal prices up.

Unlike many of its drought-prone neighbours, South Sudan is incredibly fertile and more than 90 percent of its land could be farmed. But less than 5 percent was cultivated in 2011 and this figure has fallen with two years of civil war, FAO said. (Reporting by Katy Migiro; Editing by Katie Nguyen; Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, property rights and climate change. Visit news.trust.org to see more stories.)