UNITED NATIONS, April 29 (Reuters) - U.N. Secretary-General Ban Ki-moon urged South Sudan President Salva Kiir on Tuesday to publicly call for an end to a "negative campaign" against U.N. peacekeepers and to bring to justice those responsible for attacks there on civilians and the United Nations.
In a phone call with Kiir, the U.N. chief called for "an immediate halt to the vicious fighting and the appalling killing of South Sudanese civilians," according to a statement from Ban's press office.
More than 1 million people have fled their homes since fighting erupted in December between troops backing Kiir and soldiers loyal to his sacked deputy, Riek Machar. The fighting has exacerbated ethnic tensions between Kiir's Dinka people and Machar's Nuer.
Thousands of people have been killed and tens of thousands have sought refuge at U.N. bases around South Sudan, the world's youngest country, after the violence spread.
Ban "stressed the need to ensure that the perpetrators of the completely unacceptable attack on the United Nations Mission in South Sudan (UNMISS) compound in Bor and the ethnically motivated killings in Bentiu are swiftly brought to justice."
The United Nations accused the rebels earlier this month of hunting down hundreds of people in a hospital, church and mosque in Bentiu, the capital of the oil-producing Unity state, and killing them based on ethnicity and nationality.
After that massacre, Dinka residents of Bor in Jonglei state attacked a U.N. base where about 5,000 people, mostly Nuer, were sheltering. At least 58 people were killed and nearly 100 wounded, including two U.N. peacekeepers.
Ban "urged the president to intervene personally to stop the negative campaign against UNMISS staff and issue a public statement to this end."
Negotiations between the Kiir government and rebels loyal to Machar have failed to advance since the Jan. 23 signing of a ceasefire which never took hold.
U.N. Security Council members are considering sanctions on South Sudan's warring parties.
The United States and the European Union have already threatened South Sudan with sanctions. President Barack Obama earlier this month authorized possible targeted sanctions against those committing human rights abuses in South Sudan or undermining democracy and obstructing the peace process.
(Reporting by Michelle Nichols, editing by G Crosse)