* Residents fleeing Southern Kordofan capital Kadugli - U.N.
* Kadugli airport closed to U.N. flights since Friday
* North and south leaders to hold talks in Ethiopia
* Need to agree on oil revenues, borders, national debt
(Adds Human Rights Watch, Amnesty International statements)
By Khaled Abdelaziz and Alex Dziadosz
KHARTOUM, June 11 (Reuters) - North Sudan’s army battled southern-aligned troops across the volatile Southern Kordofan border state for a seventh day on Saturday, adding to tensions ahead of talks between the northern and southern leaders.
South Sudan is due to secede on July 9, but bloodshed along the ill-defined border over the last three weeks has raised fears the two long-standing rivals will return to open conflict.
North and south have yet to agree on a number of sensitive issues before the split, including how to share oil revenues, where to draw the common border and how to split national debt.
Tensions mounted after Khartoum sent tanks and troops into the contested Abyei region on May 21. Fighting broke out in oil-producing Southern Kordofan about two weeks later and has since intensified, with artillery and aircraft used.
The U.N. mission in Sudan, known as UNMIS, said residents were fleeing Southern Kordofan’s capital Kadugli on foot and in buses and trucks to escape the fighting.
Human Rights Watch and Amnesty International said in separate statements they had received reports northern forces were searching streets and houses in Kadugli and killing suspected SPLM supporters.
The northern army has previously blamed southern or southern-aligned groups for starting fighting in Southern Kordofan and elsewhere and says it does not target civilians.
“The security situation remains of great concern. Localised fighting, sporadic artillery fire and continuing military build-up were reported during the last 24 hours,” UNMIS spokesman Kouider Zerrouk said.
Analysts see Southern Kordofan as a flashpoint because it is home to thousands of fighters, many from the Nuba mountains region, who fought Khartoum during the civil war.
The state is important to the north because it has the most productive oil fields that will be left in its control after the split, which could see Khartoum lose some 75 percent of Sudan’s 500,000 barrels per day of oil output.
Gamr Dalman, media advisor to the head of the Southern Kordofan branch of the south’s dominant party the Sudan People’s Liberation Movement (SPLM), said the north had carried out dozens of air strikes across the state over the last three days.
He said fighters shot down two northern military aircraft — a MiG-23 and an Antonov — on Friday, but there was no independent corroboration of the report. No one from the northern military was immediately available to comment.
The United Nations has estimated that between 30,000 and 40,000 people have fled Kadugli alone. Dalman put the number of displaced in the state so far at 75,000.
Southerners voted to secede in a January plebiscite promised by a 2005 peace deal that ended the last civil war. North and south Sudan fought for all but a few years since 1955 over resources, ethnicity, religion and ideology.
UNMIS spokesman Zerrouk said Kadugli’s airport had been shut since Friday morning, and that the northern army was strengthening its positions in several locations in the state.
“The closure of the airport by the (northern Sudanese Armed Forces) SAF will dangerously hamper the U.N. humanitarian operations in Southern Kordofan, as thousands of civilians are in urgent need of emergency assistance,” he said.
Tensions have been high in Southern Kordofan since a northern ruling party member, wanted by the International Criminal Court on charges of war crimes in the western Darfur region, was named winner of a gubernatorial election last month.
The south said the voted was rigged, which the north denied.
Fighting in the state came about two weeks after Khartoum occupied the fertile, oil-producing Abyei region, which both north and south claim.
The north’s President Omar Hassan al-Bashir was scheduled to meet the south’s President Salva Kiir in the Ethiopian capital of Addis Ababa on Sunday to discuss Abyei’s status and other unresolved issues, officials said.
Ethiopian Prime Minister Meles Zenawi and former South African President Thabo Mbeki were also expected to participate. (Additional reporting by Jeremy Clarke in Juba; Writing by Alex Dziadosz; Editing by Louise Ireland)