Tension and anger on Sunday gripped the Abyei region disputed by Sudan and South Sudan after the killing of a tribal chief and at least one peacekeeper, residents said, as the UN boosted security.
The Sudanese foreign ministry condemned the "isolated incident" which killed Kual Deng Majok, the top Ngok Dinka leader in Abyei.
One Ethiopian peacekeeper died and two other Blue Helmets were seriously wounded in the "attack by a Misseriya assailant on a UNISFA convoy", the United Nations said.
Sudan's Interior Ministry later said one of the wounded peacekeepers had died while the foreign ministry reported three Blue Helmets lost their lives.
The foreign ministry expressed hope that the killings will not affect improving relations with South Sudan, whose army spokesman also condemned the violence.
"It looks like Dinka are very angry," one local resident told AFP.
He reported fire burning in Abyei's town centre, where Misseriya run small shops.
A curfew was in effect, with UNISFA setting up extra checkpoints, the resident said on condition of anonymity.
The resident, who is familiar with the incident, said five Misseriya died in Saturday's skirmish.
"There is high tension" but no new fighting occurred on Sunday, 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 (the) aim of maintaining calm".
But South Sudan's army spokesman, Philip Aguer, said the killings show the 4,000-member UNISFA needs to be strengthened "so that it can provide full security".
The African Union, which has been mediating the Abyei dispute, called on Khartoum and Juba "to ensure that the current situation does not spiral out of control."
UN chief Ban Ki-moon urged both tribes and governments to "avoid any escalation of this unfortunate event," a statement said.
Abyei's status 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.
"The government of Sudan renews its commitment to all the agreements that have been signed with South Sudan," Khartoum affirmed after Majok's death.
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 when they were stopped by a group of Misseriya, a Misseriya leader said. Despite negotiations, a deadly clash erupted "when a UNISFA soldier shot one of the Misseriya who was readying his weapon," the Misseriya chief said.
Dinka are a dominant tribe in South Sudan and made up the majority of Abyei's permanent residents, but large numbers of nomadic Arab Misseriya have traditionally used the territory's pasture and water sources for their cattle.
Tensions over access to those resources have been increasing, the UN says.
After Misseriya surrounded Majok's convoy, negotiations continued "for a long time" until a Misseriya youth, shouting and armed, climbed onto the roof of Majok's car, said the Abyei resident familiar with the situation.
"At some point a bullet came from one side," triggering an exchange of fire, he said.
Majok's death is the most serious incident since Sudanese troops withdrew in May 2012 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 met deadlines they also agreed upon to set up Abyei's administrative structure, including a police service.