Seven peacekeepers were killed on Saturday during an ambush in Sudan's Darfur region, the African Union-UN Mission said, marking the worst-ever losses in the five-year history of the operation.
The attack adds to worsening violence in Sudan's far-west region and happened near the peacekeepers' base at Manawashi, north of the South Darfur state capital Nyala.
"Seven peacekeepers were killed and 17 were injured," UNAMID's acting spokesman Christopher Cycmanick told AFP.
The incident occurred about 25 kilometres (16 miles) west of another UNAMID base at Khar Abeche, Cycmanick told AFP.
"The UNAMID team came under heavy fire from a large unidentified group. Following an extended firefight, the patrol was extracted by UNAMID reinforcements", a statement said.
UNAMID did not immediately give the nationalities of the victims, but Tanzanian troops are in charge of that area.
Earlier this month three Nigerian peacekeepers were wounded and an ambulance with their patrol was shot up in Labado, east of Nyala, Herve Ladsous, the UN's Undersecretary General for Peacekeeping, said during a visit to Sudan.
The peacekeepers killed at least one attacker, he said.
More than 40 UNAMID members have died in hostile action since the mission's establishment in 2007.
But UN sources have said they were unaware of anybody previously being held accountable in Sudan for killing a peacekeeper, despite repeated UN calls for the perpetrators to be brought to justice.
In April, a Nigerian peacekeeper was killed and two others were wounded in an assault against their base east of Nyala.
At the time, local sources said that attack appeared to have been planned and carried out by government-linked forces, but authorities denied such a connection.
A UN panel of experts earlier this year reported that former members of government militias "have forcibly expressed their discontent with the current government," including through occasional cases of "direct attacks on UNAMID staff and premises".
Prior to Saturday, six other peacekeepers had been killed in attacks in Darfur since October.
Rebels have been fighting for 10 years in Sudan's far-western and have contributed to some of the unrest this year.
But UNAMID chief Mohamed Ibn Chambas has blamed inter-ethnic fighting for most of the violence, which displaced an estimated 300,000 people.
UN experts, human rights activists and tribal leaders have accused government security forces of involvement in this year's tribal fighting.
But Chambas said the nature of the disputes -- mainly competition for land, water and mineral rights -- made it hard to tell who was on which side as police and militia also had ethnic affiliations
A diverse group of critics from rebels to Darfur's top official, Eltigani Seisi, have expressed concerns about UNAMID's ability to safeguard the population, including 1.4 million displaced by Darfur's decade-long conflict.
On Saturday a humanitarian source told AFP the latest incident will make UNAMID more cautious.
"The only thing they will do in future is to make sure they stay safe, rather than investigating anything," said the source, asking for anonymity.
During his visit to Sudan this month Ladsous responded to the critics by saying that UNAMID, with about 20,000 military and police officers, "has the inherent robustness to deal with the situation."
But he admitted there have been a few cases where the peacekeepers' actions did not meet expectations.
On October 2 four Nigerian Blue Helmets were killed in an ambush near El-Geneina in West Darfur. At that time it was the deadliest attack in UNAMID history, UN sources said.
Rebels began their uprising against the Arab-dominated Khartoum regime in 2003.
Security problems have more recently been compounded by the inter-tribal fighting, kidnappings, carjackings and other crimes, many suspected to be the work of government-linked militia and paramilitary groups.