Some 34,000 people in Sudan's western Darfur region have fled fierce clashes between government forces and rebels around the mountainous Jebel Marra area, the United Nations said on Wednesday.
After several months of relative quiet in the restive region following Khartoum's announcement of a ceasefire late last year, fresh fighting erupted around Jebel Marra around 10 days ago.
Jebel Marra straddles South, Central and North Darfur states and is seen as a stronghold of the rebel Sudan Liberation Army (SLA-AW), which has been battling the government since 2003.
"Initial reports indicate that about 19,000 civilians have fled into North Darfur state, and up to 15,000 into Central Darfur state, following fighting in the mountainous Jebel Marra region," said Marta Ruedas, the UN humanitarian coordinator in Sudan.
The vast majority of those fleeing the fighting were women and children, she said.
The ceasefire was extended for a month on New Year's Eve.
Sudan's military said it is committed to the ceasefire and has only responded to rebel attacks, while the SLA-AW has said government troops and militia have tried to fight their way into Jebel Marra, claiming to have beaten back several attacks.
Ruedas said the United Nations had provided some humanitarian assistance but lacked full access to the region.
"While it is encouraging that some humanitarian assistance is being provided, clearly much more is needed," she said.
The UN-African Union Mission in Darfur (UNAMID) previously said more than 10,000 people have been displaced in the fighting, and that artillery and aerial bombardments had been used in the clashes.
Jebel Marra is one of the most isolated areas in the Darfur region, where ethnic insurgents rebelled against President Omar al-Bashir nearly 13 years ago, complaining they were being marginalised.
Bashir unleashed a bloody campaign to crush the rebels, using ground forces, jet bombers and allied militia.
The International Criminal Court indicted him on charges of war crimes, crimes against humanity and genocide related to the Darfur conflict, although he has dismissed the allegations.
New York-based Human Rights Watch said on Wednesday that government troops and militia had used "rape as a weapon of war" in previous battles in Darfur in 2014 and 2015.
"The pattern, scale, and frequency of rape suggests that Sudan's security forces have adopted this sickeningly cruel practice as a weapon of war," HRW's Africa Director Daniel Bekele said.
The watchdog called on UNAMID to do more to document allegations of abuse in Darfur.
The peacekeeping mission deployed to Darfur in 2007, although in late 2014 Khartoum told it to prepare to leave over its attempts to investigate reports of a mass rape in a North Darfur village.
More than 300,000 people have been killed in the conflict since 2003 and there are 2.5 million displaced people living in the region, according to the UN.