The United Nations said yesterday that four Nigerian peacekeepers were killed and eight wounded in an ambush in Sudan’s restive West Darfur region.

U.N. spokesman Martin Nesirky said the ambush in El-Geneina took place on Tuesday evening.

He said UN Secretary-General Ban Ki Moon “is appalled and deeply saddened” at the latest attack on peacekeepers and urges the government of Sudan “to conduct a full investigation and to ensure that the perpetrators are swiftly brought to justice.”

Darfur has been torn by conflict since 2003, when rebels took up arms against the central government, accusing it of discrimination and neglect. Violence has tapered off, but clashes continue and peacekeepers are a target.