Five people have been killed and 23 wounded in an attack by rebels in the capital of Sudan's South Kordofan state, government radio says.State media reported shelling in Kadugli, near the southern border, and blamed a rebel group suspected of planning to overthrow the government.The SPLM-North admitted to the attack but denied any civilian casualties.Rebels have been fighting in South Kordofan since last year but the state capital has been largely peaceful.South Sudan, which seceded in 2011, denies backing the rebels.Precautionary measuresA spokesman for the SPLM-N claimed responsibility for the attack. He said his men were on the outskirts of Kadugli, but that they were "not targeting the people" but the military."We have to fight back and of course to carry out our objective of removing the government," the rebels' spokesman, Arnu Ngutulu Lodi, told Reuters.A government Radio Omdurman broadcast did not say whether the casualties were civilian or military.Earlier, the Sudanese army spokesman said the SPLM-North had "tried to get inside Kadugli town and they shelled an area 6 km [four miles] east of Kadugli." He reported one fatality at the time.The United Nations said their humanitarian staff in the area had been moved to a nearby peacekeeping base "as a precautionary measure"."To our knowledge there were five mortar shells that landed in and around the town" of Kadugli, Damian Rance of the UN's Office for the Co-ordination of Humanitarian Affairs (OCHA), told AFP.Another UN worker said the shelling began at 1140 local time (0840 GMT) and lasted just over half an hour. He said one or two shells landed inside the Unicef compound but did not explode.The fighting in South Kordofan has been one of the major issues dividing Sudan and its southern neighbour over the past year.The two countries' leaders recently signed a partial peace deal aimed at reducing tensions.The rebels in South Kordofan fought with the south against the Khartoum government for two decades but after South Sudan's independence, they found themselves still in Sudan.Many of the rebel fighters are from the Nuba ethnic group and Sudan has previously denied accusations by human rights activists that its forces have targeted civilian members of the community during the conflict.