"Recent arrivals continue to speak of barbaric violence, with armed groups reportedly burning down houses with civilians inside, people being killed in front of family members, sexual assaults of women and girls and kidnapping of boys for forced conscription," the UN's refugee body, UNHCR, said in a statement on Thursday.
With the total number of refugees in Uganda topping one million, the organization estimates that it will need $674 million (576 million euros) for its aid program this year. It has so far received only around one-fifth of that amount. A fundraising summit, hosted by Ugandan officials last month, has also been unsuccessful.
'Crisis will only escalate'
"This unhappy one-million milestone must serve as a wake-up call to the international community that much more is needed from them," Sarah Jackson, an Amnesty International official in the region, said on Thursday. "With no resolution to the conflict in South Sudan in sight, refugees will continue to flee to Uganda and the humanitarian crisis will only escalate."
Over 85 percent of refugees in Uganda are women, children, and teenagers under the age of 18. South Sudanese are free to enter Uganda and work there, but the lack of funding has left activists struggling to provide food, schooling, and basic health and sanitation services to the refugee camps.
The largest of such settlements, called Bidi Bidi, 230 square kilometers (89 square miles).
Peace still far away
"Two weeks ago my husband's uncle was killed," said Stella Taji told Reuters news agency. "Since then we've been hiding in the bush. We have nothing."
The long-running civil war in South Sudan started soon after the country won its independence from Sudan in 2011. The conflict pits forces loyal to President Salva Kiir against fighters loyal to former Vice President Riak Machar, and UN's numerous attempts to stop the fighting have been unsuccessful.
In addition to one million refugees in Uganda, another million South Sudanese fled to other nearby countries, including Kenya, Ethiopia and Sudan. Another two million have been internally displaced.