Piles and piles of bodies in Bentiu

The townsfolk believed the mosque was safe. They crammed inside as rebel forces in South Sudan took control of the town from government troops. But it wasn’t safe. Robbers grabbed their cash and mobile phones. Then gunmen came and opened fire on everyone, young and old.

The U.N. says hundreds of civilians were killed in the massacre last week in Bentiu, the capital of South Sudan’s oil-producing Unity state, a tragic reflection of longstanding ethnic hostilities in the world’s newest country.

“Piles and piles” of bodies were left behind after the shootings, said Toby Lanzer, the top U.N. aid official in South Sudan. Many were in the mosque. Others were in the hospital. Still more littered the streets. The violence appears to have been incited in part by calls on the radio for revenge attacks, including rapes.

The attack, which targeted members of certain ethnic groups, was a disturbing echo of what happened two decades ago in another country in eastern Africa.

Rwanda is marking the 20th anniversary this month of a genocide that killed an estimated one million people and also saw orders to kill broadcast over the radio.

Thousands of people have been killed in violence in South Sudan since December, when presidential guards splintered and fought along ethnic lines. The violence later spread across the country as soldiers loyal to President Salva Kiir, an ethnic Dinka, tried to put down a rebellion led by Riek Machar, the former Vice-President and an ethnic Nuer.

But Mr. Lanzer told The Associated Press in a phone interview on Tuesday that the April 15-16 mass killings, carried out by Nuers, are “quite possibly a game-changer” in the conflict.

Mr. 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 litre 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.

Residents misled As rebel forces entered Bentiu last week, residents were led to believe that by entering the mosque they would be safe, Mr. 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.