Why couldn't the army or the UN stop massacres in South Kivu?

Villagers in eastern Congo have told the BBC that United Nations and government forces failed to stop the massacre of thirty-seven people.The killings happened less than 10 kilometres from UN and army barracks. Villagers were attacked last June by unknown gunmen, and since then tensions have been rising. Nine more people have been killed this month. There has long been rivalry between ethnic groups the Banyamulenge and the Bafulero fighting over land . The BBC s Maud Jullien travelled to Mutarule, in South Kivu, where the massacres took place.