The UN's top humanitarian official, Jan Egeland, was forced to flee a camp for people displaced by the Darfur conflict in Sudan after violent protests.
Darfur's rebel groups took up arms in 2003
The trouble started during a march calling for foreign troops to be sent to protect the camps, when a woman said a translator belonged to a militia.
He escaped but another interpreter, who worked for the African Union, was set upon and killed a short while later.
More than two million people have fled since fighting began in 2003.
Some of the worst atrocities, such as mass killings, rape and looting has been blamed on the pro-government Janjaweed militia.
The translator accused of being a Janjaweed fighter managed to escape with bruises despite being attacked by a mob.
But shortly after Mr Egeland's group had left, a crowd overran an African Union mission in the Kalma camp and killed one of their Sudanese interpreters.
DARFUR PEACE PLAN
Pro-government Janjaweed militia to be disarmed
Rebel fighters to be incorporated into army
One-off $300m transfer to Darfur
$200m a year for the region thereafter
Compensation for those forced to flee their homes
Regional government, if approved in a vote
Mr Egeland, the UN's Emergency Relief Co-ordinator, said he was devastated by the news.
After the violence at the camp, home to some 90,000 people, Mr Egeland returned to the nearby town of Nyala.
Mr Egeland was due to travel to the capital, Khartoum, on Monday for talks with government officials.
He earlier said it was vital that UN peacekeepers were allowed into Sudan's Darfur region to help end the humanitarian crisis.
Some 7,000 African Union peacekeepers have failed to end the violence.
However, the government and the biggest rebel group signed a peace deal on Friday, which could pave the way for Sudan to allow the UN to take over.
The BBC's Jonah Fisher in Kalma says many of the protesters said they had little faith in the new peace agreement and only after an international force is deployed could they think about returning home.
Earlier, Mr Egeland also called for aid workers to be given free access to Darfur, as laid out in the agreement.
"At the moment Darfur is slowly being strangled, it's dying in front of us," he said.
"Half of the population now has become war victims... so I believe, yes, we are turning the corner, but the whole world has to put pressure on the parties."
Mr Egeland says access for aid workers is at its worst for two years
He was speaking in the town of Gereida which is held by the rebel group which signed the peace deal, the Sudan Liberation Movement.
But two smaller rebel groups rejected the agreement.
Just a month ago, the government banned Mr Egeland from visiting Darfur.
Tens of thousands of people around Gereida have been displaced in recent weeks, and the UN has warned of an impending disaster.
The three-year conflict has killed about 200,000 people and left about two million homeless.
Aid organisations say the conflict has created one of the world's worst humanitarian crises.
Money for the world's largest aid operation is running out. Rations for May have been cut in half .
The rebels took up arms in 2003, accusing the government of discriminating against the black African residents of Darfur.
Pro-government Arab militia then launched a campaign, described as "genocide" by the US.
The Sudan government denies backing the Janjaweed militias.