Five people have been killed and more than 20 wounded after anti-government fighters shelled the capital of Sudan's South Kordofan state, according to official radio.
Sawarmi Khaled Saad, Sudan's army spokesman, could not confirm the figure and gave a lower toll, saying that one woman died from Monday's rebel firing around Kadugli.
"This morning a group from SPLM-North tried to get inside Kadugli town and they shelled an area 6km east of Kadugli. As a result of this a woman was killed and three citizens injured," he said.
Saad said stability had now been restored.
"Five people are martyred and 23 wounded because of the SPLM-North shelling of Kadugli," Radio Omdurman reported on Monday in a text-message news alert, which gave no source for the information.
The UN and local residents said the town itself had been hit.
Fighters from the Sudan People's Liberation Movement-North (SPLM-N) acknowledged the attack but said they do not target civilians.
"Yes, this is our people who have attacked," the rebels' spokesman, Arnu Ngutulu Lodi, said.
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"We are not far from Kadugli. We are just on the outskirts of Kadugli."
Lodi had no information on casualties or further details of the attack. He said his forces "are not targeting the people" but the military.
"To our knowledge there were five mortar shells that landed in and around the town," Damian Rance of the UN's Office for the Co-ordination of Humanitarian Affairs (OCHA) said.
The army has been battling SPLM-N rebels since June last year.
Rance said all UN staff in Kadugli, both Sudanese and foreign, were moved "as a precautionary measure" to a base between Kadugli and the local airport.
The base is used by a UN peacekeeping mission, UNISFA, which operates in the Abyei region contested by Sudan and South Sudan.
UN staff 'all safe'
Rance could not say how many UN personnel were involved, but the UN's World Food Programme said that 15 Sudanese staff from its office, eight of their family members, and one international employee were taken to the UNISFA base.
"They are all safe," a WFP official said.
The incident coincided with the start of talks in Kadugli between the ruling National Congress and other political parties about how to end the war which the UN says has displaced or severely affected hundreds of thousands of people.
Saad, the Sudanese army spokesman, accused rebels of trying to disrupt the meeting but Lodi denied that, saying the attack came within their strategy of trying to overthrow the Khartoum regime.
The war began with fighting in Kadugli but since then the town has remained in government hands, although there has previously been combat nearby.
Ethnic minority fighters from the SPLM-N had fought alongside rebels from southern Sudan who waged a 22-year civil war which ended in a 2005 peace deal leading to South Sudan's independence last year.
Agreement in doubt
Sudan and South Sudan signed late last month deals on security and co-operation that they lauded as ending their countries' conflict.
The neighbours fought in their border regions in March and April, raising fears of wider war and leading to a UN Security Council resolution ordering a ceasefire and the settlement of unresolved issues, under African Union mediation.
The deals signed include a key agreement on a demilitarised border buffer zone, where troops must withdraw 10km from the de facto line of control along the undemarcated frontier.
The buffer zone is also designed to cut support for fighters in South Kordofan and Blue Nile state, where the SPLM-N has also been fighting.
Sudan accuses South Sudan of backing those fighters, and the South in turn accuses Sudan of arming rebels in its territory.