KHARTOUM (AFP) -- The first UN food aid has been allowed into Sudan's war-torn Blue Nile state in a "major breakthrough," the World Food Programme said on Thursday, after severe government restrictions.

"This is the first time that the agency has distributed food assistance since the conflict broke out in September 2011," the WFP said.

The war in Blue Nile and another state, South Kordofan, has occurred largely out of world view as Sudan, citing security concerns, tightly constrained the movement of foreign aid workers, diplomats and reporters seeking to visit the region.

"While we continue to strive for access to all areas, this is still a major breakthrough which will enable us to assist those who continue to be displaced by the conflict or those who have decided to return to their homes and are in dire need of food assistance," WFP Sudan director Adnan Khan said in a statement.

In South Kordofan, authorities had already allowed WFP to distribute food in a limited area, but rebel zones in both states remain off limits.

Allowing WFP to begin work in Blue Nile is the latest sign of an easing of tensions since Sudan and South Sudan finally settled on detailed timetables in early March to implement crucial economic and security pacts.

Khartoum had accused the South Sudanese government of backing rebels of the Sudan People's Liberation Movement-North (SPLM-N) in Blue Nile and South Kordofan.