Lanzer said thousands of civilians from several ethnic groups are streaming to the U.N. peacekeeping base in Bentiu because many believe more violence is coming. The base now holds 22,000 people - up from 4,500 at the start of April - but can supply only one liter of water per person per day. Some 350 people must share one toilet.
"The risk of a public health crisis inside our base is enormous," he said.
Raphael Gorgeu, the head of Doctors Without Borders in South Sudan, said people will die inside the U.N. base in the coming days because of the water and sanitation situation.
As rebel forces entered Bentiu last week, residents were led to believe that by entering the mosque they would be safe, Lanzer said, citing accounts from survivors. But once inside they were robbed of money and mobile phones and a short while later gunmen began killing, both inside the mosque and inside the city hospital.
The U.N. hasn't spelled out clearly who exactly the victims were, but it is likely that ethnic Dinkas were among the dead. If you were not Nuer, then nothing could save you. And even Nuers who refused to take part in the attacks were killed, according to the U.N., as were former residents of the Darfur region of Sudan.
The gunmen killed wantonly, including children and the elderly, Lanzer said.
U.N. officials began helping to clear the bodies from the streets and city buildings after the bloodshed. Lanzer arrived in Bentiu on the third day of that operation but still counted 150 bodies. He said the U.N. is documenting the killings and will soon have "a pretty good grasp" on the precise number killed.
