Khartoum - Gunmen ambushed and killed a district chief in Sudan's South Darfur, the state governor said on Sunday, after tribal clashes elsewhere in the troubled region reportedly left 18 dead.
Abdullah Yasin, the top government official in Katayla district, "was ambushed by armed men and lost as a martyr," South Darfur Governor Adam Mahmoud told Al-Shurooq television.
"They are outlaws," Mahmoud said, adding that government troops were searching for the attackers.
Anti-government rebels were not in the area, which is southwest of the state capital Nyala, the governor said.
Rebel violence is no longer the main source of unrest in Darfur, an area about the size of France.
Insurgents from black tribes rose up 11 years ago against what they said was the domination of Sudan's power and wealth by Arab elites.
In response, the government-backed Janjaweed militia rode in on horseback, shocking the world with atrocities against ethnic Africans.
Since the start of that conflict the government has encouraged the formation of armed tribal militias.
But with the government now in economic crisis, "financial and logistical constraints have thus forced the Janjaweed, militias and tribal armed groups to advocate autonomy and operate independently of government control when it suits them to do so," a February report by a United Nations panel of experts said.
The militias in search of resources have turned on each other, and sometimes against the government, while violent crime has increased.
In the latest inter-communal battle, fighting between two Arab tribes killed 18 people, a resident said on Sunday, adding to a growing toll.
The fighting occurred outside Ed Daein, the capital of East Darfur, said the resident who is a member of the local Rezeigat tribe.
"Yesterday the clash began when a Maaliya killed a Rezeigat. The Rezeigat gathered themselves for revenge but the Maaliya surrounded them and killed 18," he said, declining to be identified for security reasons.
A member of the rival Maaliya tribe said a rocket-propelled grenade destroyed a Rezeigat pickup truck used as a troop-carrying vehicle.
"I saw the Rezeigat taking away their bodies," from the vehicle, he said.
Hundreds of Rezeigat were gathering for retaliation and "a big battle might happen today or tomorrow," another resident said.
Battles between the Rezeigat and Maaliya in East Darfur last August killed 190 people, the UN said at the time.
"It is important to note that during those clashes the government was unable, or unwilling, to stop the fighting," the UN panel of experts said.
Hundreds more people died in battles between other tribal groups, most of them Arab, in Darfur last year.
Inter-communal fighting has continued this year in Darfur and also in West Kordofan, which adjoins East Darfur.
A battle last week between two sub-groups of the Misseriya tribe killed 150 people and wounded 100 more near an oil-drilling site in West Kordofan, state-linked media reported.