The United Nations on Sunday voiced concern over the humanitarian situation of some 50,000 people displaced by fighting in southern Sudan's Upper Nile regions.

"Since early March, at least 50,000 people have been displaced by militia attacks and clashes between government forces and Sudan People's Liberation Army (SPLA) rebels in the area -- also known as Shilluk Kingdom," the Office of the UN Humanitarian Coordinator for Sudan said in a statement.

Fighting in Upper Nile pits militia loyal to former rebel leader Lam Akol, who in mid-1990s defected to the government side but recently rejoined the SPLA, against pro-government fighters opposed to a return to SPLA fold.

"Villages have been burnt down, while looting and rapes have gone on, civilian infrastructures, including schools and clinics, have been destroyed and international non-governmental organisations (NGOs) compounds in Nyilwak have also been burnt in attacks," added the statement released in Nairobi.

It said that UN and NGOs, grouped under Operation Lifeline Sudan (OLS), which suspended relief operations in the region on March 30, cannot access the war areas because of insecurity.

"The OLS, working in SPLA-held areas, has been forced to suspend operations and relocate staff several times this year due to the conflict," the statement said.

"Details of the humanitarian impact outside the government-held Malakal garrison are difficult to obtain, due to a lack of sufficient security to mount assessments," it said, pointing out that relief operations were going on only inside Malakal.

It urged the warring sides to refrain from attacking civilian targets in order to protect lives, property and human rights of civilians.

Last month, the German aid group Hoffnungszeichen (Sign of Hope) accused pro-Khartoum militias of committing atrocities against civilians, saying the fighters "had killed people, torched homes and stolen cattle."

Acting US Secretary of State for African Affairs Charles Snyder also urged Khartoum and the SPLA to respect a ceasefire they signed in January 2002 - Sapa-AFP.