Rebels killed a Sudanese state official and seven other people in the oil-producing border state of South Kordofan, the state news agency said on Friday, the most senior official to be killed since fighting began in the region a year ago.

Sudan's border regions with South Sudan have been mired in violence since the southern nation seceded a year ago under a 2005 peace deal that ended decades of civil war.

Hundreds of thousands of people have fled their homes in South Kordofan and nearby Blue Nile state since the fighting broke out, the United Nations has said.

The state SUNA news agency said Ibrahim Balandiya, South Kordofan's parliament speaker, was attacked between two villages in the region. Another state official, three drivers and a photographer were among those killed, SUNA added, in an attack it blamed on "remnants of the popular army".

SUNA was referring to rebels from the Sudan People's Liberation Movement-North (SPLM-N), who were not immediately available for comment.

The SPLM-N fighters in South Kordofan are among tens of thousands who sided with the South against Khartoum during Sudan's civil war, but were left north of the border under the peace pact.

Last year, the insurgents formed an alliance with other rebels in Sudan's western Darfur region with the aim of toppling the government of President Omar Hassan Al-Bashir, who is facing an upsurge in popular protests.

The rebels say their border regions have been left underdeveloped and marginalised by an Arab elite in Khartoum.

Sudan has said it is determined to restore order to the territories and accuses its old foe South Sudan of backing the insurgents, something Juba denies.