More than 60 people have been killed in ethnic clashes in Sudan's arid Darfur region, over land producing gum arabic, the police have said.
The gum is a food additive, used in soft drinks, and an adhesive.
The deaths are the result of an ongoing dispute between two ethnic groups in South Darfur, over pasture and acacia trees, from which the gum is cut.
The Gemir group accuses the Beni-Halba community of trying to take away land it has owned for more than 300 years.
State police said there were 64 deaths and scores of wounded in fighting in Katila, on Tuesday, involving four-wheel drives, horses and guns.
Gum arabic is one of Sudan's most important export products.
For years, Sudan has had a virtual monopoly on it.
But part of the output is now being smuggled over the border into Chad to be sold for cash.
Some Arab groups were armed by Khartoum from 2003, in a bid to end an insurgency by mainly non-Arab rebels.
But they have since turned their weapons on each other to try to seize resources such as gold and the gum arabic, which is bought by international companies, including Coca Cola.
The UN said there were similar clashes in the area last week, Reuters news agency reports.
"An estimated 6,500 people fled Katila and sought refuge in Tulus [in South Darfur]," it quotes the UN statement as saying.
Around 300,000 people have been displaced since the start of this year across Darfur.
More than 500 were killed in clashes between two tribes fighting for control of a gold mine in North Darfur in January and February.
Events in Darfur are difficult to verify because Sudan restricts travel by journalists, aid workers and diplomats.