Shooting and shelling broke out in the main city of Sudan's oil-producing South Kordofan state near the border with South Sudan on Monday, witnesses said.
Sudan's army has been battling rebels in the state for over a year, but the capital Kadugli has been mostly isolated from the fighting.
"There was shelling in Kadugli today. It started at around 1140 and stopped at around 1215," said Ray Torres, officer in charge at UNICEF, which has a compound in Kadugli.
One or two shells landed inside the UNICEF compound but did not explode, Torres said, adding that one women had been injured by a rocket explosion outside the compound. Two witnesses in the area confirmed the shelling.
Rebel fighting in South Kordofan has been a major source of contention between Sudan and South Sudan since they split apart in July last year under a 2005 peace deal that ended decades of civil war.
The insurgents - known as the Sudan People's Liberation Movement-North (SPLM-N) - fought as part of the southern rebel army during the war and Khartoum accuses the new nation's government of continuing to back them. South Sudan denies the charge.
Rebel spokesman Arnu Lodi said the SPLM-N had troops positioned around Kadugli, but could not immediately comment on whether they were behind the shelling on Monday.
Facing international pressure, Sudan and South Sudan signed a deal last month to secure their border but indirect talks between Khartoum and the SPLM-N have made no visible progress.
(Reporting by Khalid Abdelaziz, Ulf Laessing and Alexander Dziadosz; Editing by Rosalind Russell)