The United Nations has opened a new humanitarian corridor through Sudan to save thousands of people facing famine in South Sudan.

The development follows an agreement signed on Sunday between the UN and Khartoum, allowing the flow of aid to South Sudan's border Unity State, considered one of the areas most affected by war and famine in the young state.

Unity State boasts of rich oil reserves but has witnessed the bloodiest battles between the South Sudan warring factions since December 2013.

The route runs from El-Obeid, the capital of North Kordofan State, through Heglig to Rebcona, then Bentiu in Unity State.

The Sudanese Aid Commissioner, Ahmed Mohamed Adam said: "We invited you today to announce the acceptance of the Sudanese government to open a new corridor from El-Obeid, Heglig, Rebcona and Bentiu in order to deliver aid to Unity State and to the greater Bahr al-Ghazal, which are among the most affected areas by the famine."

The UN humanitarian co-ordinator in Sudan, Marta Ruedas, said that the past three months had witnessed an unprecedented flow of refugees from South Sudan into Sudan.

“We have been receiving more refugees than ever before and it is a great concern that these people are coming to us in very poor conditions,'' said Ms Ruedas. "They are leaving South Sudan because they don’t have food and they don’t have enough security."

She said that the delivery of the aid to Unity State would start within days.

“We will be taking advantage of this new possibility. This new corridor to Bentiu will be starting the delivery of assistance this week and we look forward to collaboration for success," she said.

The UN earlier this month announced that more than 30,000 South Sudanese had fled the famine, crossing the border into Sudan.