UN leader Ban Ki-moon condemned South Sudan's army and opposition rebels Tuesday for stealing food and humanitarian supplies as the country's conflict escalates.
Ban expressed alarm at the growing death toll in the month-old confrontation between President Salva Kiir and former vice president Riek Machar and insisted UN peacekeepers would not help either side.
The UN secretary-general "strongly condemns the commandeering of humanitarian vehicles and the theft of food stocks and other relief items by both government and anti-government forces," said his spokesman Martin Nesirky.
Ban hit out hours after the UN mission reported dozens of people who took refuge at a UN compound had been wounded in fighting between Kiir and Machar's forces.
The two sides were engaged in "heavy fighting" near the Malakal base in Upper Nile state, Nesirky said earlier. Stray bullets from heavy machine guns and tanks hit some of the 20,000 people who have taken shelter in the compound.
The South Sudan government said earlier that more than 200 people fleeing Malakal died when an overcrowded ferry capsized.
"The secretary-general is alarmed by the rising number of fatalities resulting from the continuing fighting in South Sudan," including the ferry disaster, said Nesirky.
"He is also deeply concerned about the rising number of displaced people in the country, which surpassed 400,000 this week, and the challenges humanitarians are facing in providing life-saving assistance."
Ban made a new appeal for a ceasefire to give a chance to negotiations brokered by the East African region's Intergovernmental Authority on Development.
"He reiterates that those responsible for attacks against civilians, humanitarian workers and UN personnel will be held accountable, and that the United Nations will continue to actively protect civilians applying strict impartiality," said Nesirky.
The United Nations had provided limited logistical assistance to the government Sudan People's Liberation Army but this was halted after the December 15 outbreak of hostilities, according to UN officials.
The International Crisis Group and other aid groups estimate that up to 10,000 people have been killed in the fighting.
The UN says 65,000 people have taken refuge in UN camps across the country and more than 430,000 have fled to Uganda and other neighboring countries.