Tension and anger on Sunday gripped the Abyei region disputed by Sudan and South Sudan after the killing of a tribal chief and a peacekeeper, residents said, as the UN boosted security.
UN Secretary General Ban Ki-Moon called for calm after the Ngok Dinka chief Kual Deng Majok and the Ethiopian peacekeeper died in an "attack" by a Misseriya tribesman in the region on Saturday.
"It looks like Dinka are very angry," one local resident told AFP.
He reported fire in Abyei's town centre, where Misseriya run small shops.
A curfew was in effect, with the UN Interim Security Force in Abyei setting up extra checkpoints trying to restrict movement and prevent gatherings, said the resident on condition of anonymity.
The resident, who is familiar with the incident, said five Misseriya also died in Saturday's skirmish.
"There is high tension and all sides are alert, ready for anything," Mohammed Al-Ansari, a Misseriya chief in Abyei, told AFP.
The UN humanitarian coordinator for South Sudan, Toby Lanzer, said on Twitter that UNISFA was "expanding patrols with aim of maintaining calm".
UN chief Ban urged both tribes as well as the governments of Sudan and South Sudan to "avoid any escalation of this unfortunate event," a statement from his spokesperson said late Saturday.
The United Nations said the "attack by a Misseriya assailant on a UNISFA convoy" also seriously wounded two of its peacekeepers.
The status of Abyei has not been resolved despite steps which Sudan and South Sudan have taken since March to normalise their relations in other areas, after months of intermittent clashes along their undemarcated frontier.
Abyei's status was the most sensitive issue left unsettled when South Sudan separated from Sudan in 2011.
The territory 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.
Majok was heading north from Abyei town with UNISFA peacekeepers, who are the only authority in the area, when a group of Misseriya stopped them, another Misseriya leader said.
Despite negotiations, "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 with UNISFA commander Yohannes Tesfamariam, who was unhurt, said the Abyei resident familiar with the situation.
The Nomadic Arab Misseriya, who migrate through Abyei with their cattle, wanted to know why a Dinka was being taken through their zone.
Dinka are a dominant tribe in South Sudan and made up the majority of Abyei's permanent residents but large numbers of Misseriya have traditionally used the territory's pasture and water sources for their animals.
Negotiations continued "for a long time" until a Misseriya youth, shouting and armed with a weapon, climbed onto the roof of Majok's car, the resident said, declining to be named.
"At some point a bullet came from one side," triggering an exchange of fire but it is unclear who shot first, he said.
A Dinka leader said Majok "was attacked by Misseriya" in the incident which also killed another Dinka.
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.
While Sudan and South Sudan have been implementing timetables set out in March for restoring relations, they have not adhered to deadlines they also agreed upon to set up Abyei's administrative structure, including a police service.
Ban warned in late March that "the potential for intercommunal violence is significant" in Abyei.