Four Nigerian peacekeepers have been killed and eight wounded in an ambush in Sudan’s restive western Darfur region, the United Nations says.

UN spokesman Martin Nesirky said the ambush on a United Nations-African Union peacekeeping patrol in El-Geneina took place on Tuesday night.

UN Secretary General Ban Ki-moon called on Sudan to conduct a full investigation into an attack that killed the peacekeepers.

Nesirky said Ban was “appalled and deeply saddened” by the ambush of a patrol by UN-African Union peacekeepers in El Geneina, West Darfur.

“The secretary general urges the government of the Sudan to conduct a full investigation and to ensure that the perpetrators are swiftly brought to justice,” Nesirky said.

Ban “expresses his condolences to the government of Nigeria and to the families of the fallen peacekeepers and UNAMID,” he said.

The peacekeeping force, which numbers 23,500, has been deployed in Darfur since 2007 in an attempt to end hostilities between rebels and the Sudanese government.

The 15-member UN Security Council also condemned the ambush.

It called on the Sudanese government to “swiftly investigate the incident and bring the perpetrators to justice.”

The council reiterated its support for the UN peacekeeping mission in Darfur and called on all parties there to co-operate with it.

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 remain a target.