Humanitarian organizations are warning of a serious food crisis expected to grip South Sudan later this year as upcoming rainy reason, combined with widespread violence, would greatly hamper their ability to deliver food to those in need, a UN spokesman told reporters  Friday.

"The looming rainy season could also make roads impassable, limiting aid organizations' ability to reach people," UN spokesman Stephane Dujarric said at a daily news briefing here, citing reports of the UN Office for the Coordination of Humanitarian Affairs (OCHA). "An estimated 7 million people in South Sudan are considered to be at risk of food insecurity, including 3.7 million people at high risk."

Humanitarian agencies plan to reach some 3.2 million of the most vulnerable people with assistance by June, said the spokesman, adding that they have so far aided more than 1 million people across the country.

Earlier this month, the United Nations Mission in South Sudan said that since hostilities erupted between the government and opposition forces in December, an average of 75,000 civilians have sought refuge in UN bases across the country.

John Ging, operations chief for the OCHA, said here last month that five million people were in need of assistance, and UN agencies were having trouble pre-positioning food stocks before the onset of the rainy season. The downpours will make already challenging roads even more difficult to navigate and force agencies to airdrop food aid, which will cost more.