By Elias Biryabarema
KAMPALA, April 23 (Reuters) - Uganda's army, backing its neighbour South Sudan against a four-month-old rebellion, said on Wednesday U.N. peacekeepers should have done more to stop insurgents slaughtering hundreds of civilians there last week.
Uganda sent troops into South Sudan shortly after fighting broke out between soldiers loyal to President Salva Kiir and his sacked deputy Riek Machar in mid-December.
In the latest major violence in the increasingly ethnic conflict, rebels hunted down men, women and children taking refuge in a mosque, church and hospital in oil town Bentiu where the U.N. has a base, according to a report from the global body.
The rebels denied carrying out the attack, which has drawn international outrage. The White House said it was horrified.
About 22,000 people took refuge in the U.N. base in the town, the capital of the oil producing Unity State, after the killings on Tuesday last week.
"It is disturbing that civilians are being killed in the backyard of a U.N. mission," Ugandan military spokesman Paddy Ankunda told Reuters.
"There are thousands of U.N. soldiers in the country and you have hundreds killed under their noses ... The United Nations ought to do more to stop these crimes," he said.
A U.N. spokesman in the South Sudanese capital Juba did not immediately respond to an emailed request for a comment.
The violence has spread across the country, often along ethnic faultlines, pitting Kiir's Dinka people against Machar's Nuer group.
The rebels have repeatedly called for the withdrawal of Ugandan troops, which their leader Riek Machar says is all that has prevented his anti-government forces from seizing the capital.
Uganda's deployment has raised alarm among some regional neighbours and Western capitals. The Ugandan government said it would pull its forces out when a regional force was deployed to enforce a ceasefire - but that force has not yet materialised.
"We cannot allow the killings of civilians. These sort of atrocities demonstrate what would happen if we were not there," Ankunda said.
The U.N. mission in South Sudan, known as UNMISS, has approximately 8,500 military peacekeepers and police deployed in a country the size of France with a population of some 11 million.
Rebel spokesman Lul Ruai Koang denied responsibility for the slaughter, blaming government forces for the killings.
More than 1 million people have fled their homes since the fighting broke out in the world's youngest country.
In Bentiu, bulldozers buried the dead in mass graves.
White House spokesman Jar Carney described the violence as an "abomination" and said both Kiir and Machar must make clear that attacks on civilians are unacceptable. (Additional reporting by Carl Odera in Nairobi; Writing by Richard Lough)