Five African Union peacekeepers have been killed in an attack in Sudan's western Darfur region, officials say.
The African Union force is struggling to halt the violence
AU spokesman Noureddine Mezni said the Senegalese soldiers were guarding a watering point near Chad when attacked.
It is the heaviest single loss in an attack since the 7,000-strong force first deployed in 2004.
A BBC correspondent in Khartoum says a helicopter ferrying senior AU military officials to El-Fasher was also shot at in a separate incident.
The four-year Darfur conflict between rebels and pro-government Arab militia has seen more than 200,000 people killed and at least 2.4 million displaced.
The AU says it is concerned about the increasing level of violence against the force.
The BBC's Jonah Fisher in Khartoum says the AU peacekeepers are overwhelmed by the complexity and scale of the conflict in Darfur.
Sudan has rejected plans to allow a large UN force to be deployed to support the overstretched AU mission in Darfur.
"We strongly condemn this cowardly attack against the very people who are working hard to achieve peace in Darfur," Mr Mezni said.
"It was totally unprovoked."
Our reporter says the AU have never had such a bad day.
On Sunday evening, four of the men guarding the water point were killed on the spot and a fifth seriously injured when they came under attack.
Attempts to evacuate the injured man were halted by the weather and he died on Monday morning.
Mr Mezni, the AU spokesman, refused to say which of Darfur's many armed groups had targeted the peacekeepers, but he said three of the attackers had also been killed.
In the other incident, the helicopter was shot at five times but no one was injured.
The AU is investigating the attack, but the implications are that the rebel group operating at Zalengei where the helicopter came under fire is responsible, our correspondent says.
The attacks came amid mounting ethnic unrest in Darfur, where some 60 members of an Arab tribe were killed at the weekend.
The UN humanitarian co-ordinator John Holmes has warned of an imminent humanitarian collapse in Darfur that may endanger tens of thousands of refugees.
Two weeks ago, Rwanda warned it would withdraw its AU troops from Darfur unless they get more logistical support. It said the troops were too poorly equipped to protect lives in the volatile region.
A total of 15 AU peacekeepers have been killed since they were deployed.