By Denis Dumo

JUBA (Reuters) - Up to 4.8 million people in South Sudan face severe food shortages in coming months, the highest level since a conflict erupted more than two years ago, U.N. agencies said on Wednesday.

Clashes have continued to flare in South Sudan even though warring factions signed a peace deal in August last year to end the conflict that erupted in December 2013.

But the deal has only been implemented slowly, leaving the country's economic crisis to deepen. Rains at this time of year add to the challenge of supplying those in need by making many roads impassable. Most roads in the area are just dirt tracks.

"The deteriorating situation coincides with an unusually long and harsh annual lean season, when families have depleted their food stocks and new harvests are not expected until August. The level of food insecurity this year is unprecedented," the U.N. agencies said in a joint statement.

The U.N. World Food Programme, one of three agencies behind the statement, said it expected to assist 3.3 million people this year with emergency food assistance, life-saving nutrition support and other aid.

"We are very worried to see that food insecurity is spreading beyond conflict areas as rising prices, impassable roads and dysfunctional markets are preventing many families, even those in towns and cities, from accessing food," said Serge Tissot, representing the U.N. Food and Agriculture Organisation.

The conflict in South Sudan, which pitted President Salva Kiir against his former deputy Riek Machar, killed more than 10,000 people and displaced more than 2 million from their homes, with many fleeing to neighboring countries.

Machar returned to Juba in April to take up the post of first vice president, similar to the position he had left.

The U.N. agencies said in the last few months 100,000 people had fled South Sudan to Sudan, Kenya, the Democratic Republic of Congo and Uganda. It said this figure would rise to 150,000 by the end of June.

South Sudan's economy, already in a dire state before the fighting erupted, has faced further pressure. Plunging oil pries have hit the biggest source of government revenues, while conflict has reduced production sharply.

Inflation stood at 295 percent year-on-year in May, up from 266.4 percent a month earlier, driven higher largely by food and drink prices, figures from the statistics office showed.

(Writing by George Obulutsa; Editing by Edmund Blair and Gareth Jones)