High tension on Sunday gripped the Abyei region disputed by Sudan and South Sudan after the killing of a top tribal chief and an Ethiopian peacekeeper, a local leader said.
United Nations Secretary General Ban Ki-moon called for calm after the Dinka chief and the peacekeeper died in an "attack" by a Misseriya tribesman in the region on Saturday.
"This morning Abyei is calm but there is high tension and all sides are alert, ready for anything," Mohammed Al-Ansari, a Misseriya chief in Abyei, told AFP.
Ban urged "the governments of Sudan and South Sudan and the Ngok Dinka and Misseriya communities to remain calm and avoid any escalation of this unfortunate event," a statement from his spokesperson said late Saturday, condemning the killings.
Leaders of both rival tribes earlier confirmed to AFP that Kual Deng Majok, paramount leader of the Ngok Dinka in Abyei, had been killed on Saturday.
The UN said one Blue Helmet from its Interim Security Force in Abyei (UNISFA) was also killed and two seriously wounded "in an attack by a Misseriya assailant on a UNISFA convoy".
The status of the Dinka-dominated area 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.
Another Misseriya leader, based just outside Abyei in Sudan's South Kordofan state, on Saturday said Majok was heading north from Abyei town with UNISFA peacekeepers, who are 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", an Abyei resident familiar with the incident 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, adding a curfew took effect after the killings.
A Dinka leader also confirmed the death of Majok, saying "he was attacked by Misseriya" in the incident which also killed another Dinka.