According to Ban's spokesman, Martin Nesirky, all the victims, from the African Union-United Nations Mission in Darfur (UNAMID), had South African nationality.

"The secretary general urges the government of the Sudan to conduct a full investigation and to ensure the perpetrators are brought to justice," a statement from Ban said.

"The secretary general expresses his condolences to the government of the Republic of South Africa, UNAMID and to the family of the fallen peacekeeper."

A joint statement from the 15 members of the UN Security Council condemned the attack in the strongest terms, and called on the Sudanese authorities "to swiftly investigate the incident and bring the perpetrators to justice."

Wednesday's ambush occurred while a UNAMID convoy of military, police and civilian personnel was heading to assess the situation following recent reports of violence near the flashpoint village of Hashaba, the mission said.

Hashaba is in Kutum district, the scene of unrest since early August when a district chief was shot dead during a carjacking attempt.

It was the second deadly ambush this month involving UNAMID peacekeepers. Four Nigerian UNAMID peacekeepers were killed on October 2 in an attack near El-Geneina, in West Darfur state.

UNAMID has been in Sudan's far-western Darfur region for more than four years with a mandate to protect civilians in a region where rebel-government clashes, banditry and inter-tribal fighting continues, though violence is less than when rebels began an insurrection nearly a decade ago.

Ethnic African rebels rose against the Arab-dominated Khartoum government in 2003. In response, the government unleashed state-backed Janjaweed Arab militia in a conflict that shocked the world and led to allegations of genocide.

The United Nations estimates at least 300,000 people died, but the government puts the toll at 10,000.

An estimated 1.7 million people are still living in camps for the displaced, it says.

The United States says more than 70 civilians died in September from fighting and aerial bombardments between rebels and Sudanese government forces.

Much of the Darfur unrest now is linked to pro-government Arab groups, which fight among themselves as well as against the regime, humanitarian sources have said.

With more than 22,000 international troops and police officers, UNAMID, the largest peacekeeping operation in the world, has a budget of about $1.4 billion for 2012-13.