The top tribal chief in the flashpoint Abyei region disputed by Sudan and South Sudan was killed Saturday in an incident involving a rival tribe, leaders from both groups said.
United Nations peacekeepers were also wounded, an Abyei resident familiar with the situation said, adding a curfew had been declared in the area.
"Today the top Dinka leader, Kual Deng Majok, was killed... in Abyei after he was attacked by Misseriya (tribesmen)," a Dinka official told AFP, requesting anonymity.
"One of his people accompanying him was also killed."
A Misseriya chief also confirmed the death, saying Majok "was killed today".
Majok's death can only inflame tensions in the Dinka-dominated area whose status has not been resolved despite steps which Sudan and South Sudan have taken since March to normalise their relations, after months of intermittent clashes along their undemarcated frontier.
Abyei's status was the most sensitive issue left unresolved when South Sudan separated in 2011.
The Misseriya leader, based just outside Abyei in Sudan's South Kordofan state, said Majok was heading north from Abyei town with peacekeepers from the UN's Interim Security Force for Abyei (UNISFA), the only authority in the area.
"A group of Misseriya stopped the convoy and started negotiations. Then a clash happened when a UNISFA soldier shot one of the Misseriya who was readying his weapon," said the Misseriya chief who asked to remain anonymous.
During the resulting clash, "the Dinka leader's car was hit by an explosion and he and his driver were killed".
Majok was travelling in the late afternoon with UNISFA commander Yohannes Tesfamariam "to see the situation on the ground", the Abyei resident familiar with the situation said.
Nomadic Arab Misseriya, who migrate through Abyei with their cattle, surrounded the small convoy when it entered a Misseriya area, the resident said, declining to be named.
They wanted to know why a Dinka was being taken through their zone, and negotiations continued "for a long time", with UNISFA calling for reinforcements, the resident said.
At some point gunfire broke out, "and they shot the car of the Dinka chief", he added, without specifying who opened fire.
"They are saying there are many casualties," including several dead Misseriya, said the resident.
He said Majok "was attacked" and wounded but he could not confirm his death.
The UNISFA commander was not hurt, the resident added.
He described the incident as the Misseriya's response to tensions last November when a group of Misseriya leaders who went to Abyei town to meet the UNISFA commander were harassed and stoned by Dinka youths.
One Dinka was killed when peacekeepers opened fire.
The death of Majok is the most serious incident since Sudanese troops withdrew in May last year to end a year-long occupation that forced more than 100,000 people to flee Abyei towards South Sudan.
Abyei was to hold a referendum in January 2011 on whether it belonged with the north or South, but disagreement on who could vote stalled the ballot.
The African Union has since proposed that a referendum be held this October.
Dinka would have the right to vote, along with Sudanese with "permanent abode" in the Abyei area.
Misseriya object to that plan.
Sudan and South Sudan have been implementing the timetables they agreed to in March for resuming the flow of oil between them, re-opening border crossings, establishing a demilitarised border zone and other measures.
But timelines they also agreed upon to set up Abyei's administrative structure, including a police service, have not been adhered to.