The UN said today that six aid workers have been killed in an ambush in South Sudan. It is the latest such attack in the country suffering a famine blamed on brutal civil war. <br/><br/>A humanitarian source working in the country told a news agency that the victims, three Kenyans and three South Sudanese working for a local aid group, were travelling from the capital Juba to the eastern town of Pibor in a convoy when the attack took place yesterday.<br/>'<br/>The source said on condition of anonymity that their car was stopped by unknown assailants and they were taken from the vehicle and shot and killed. <br/><br/>Three years of civil war in South Sudan have seen warring parties deny access to aid, attack humanitarian workers and loot relief supplies.<br/><br/>The conflict has displaced about 2.5 million people from their homes and fields and created a devastating humanitarian crisis, including a famine affecting 100,000 and threatening another one million.