Three Indian peacekeepers have died in an attack on a United Nations compound in South Sudan's Jonglei state, India's UN envoy Asoke Mukerji says.
Rebels from the second-largest ethnic group, the Nuer, stormed the base on Thursday, targeting civilians of the majority Dinka ethnic community, the BBC reported.
South Sudan has been in turmoil since President Salva Kiir accused former deputy Riek Machar of mounting a coup.
The unrest, which first broke out on Sunday in capital city Juba but has since spread, has claimed about 500 lives.
Mr Kiir, who is a Dinka, has blamed the violence on a group of soldiers who support Mr Machar, a Nuer.
The president accuses them of trying to take power by force on Sunday night in a coup attempt by Mr Machar - a claim the former vice president denies.
Mr Mukerji announced the Indian troops' deaths at a UN peacekeeping meeting in New York.
There were 43 Indian peacekeepers at the UN compound in the town of Akobo where the attack took place.
A UN spokesman said the attackers, mainly youths, had targeted 32 Dinka civilians who had sought refuge at the base. Security at the compound has been increased.
The UN expressed worry about a possible civil war between the Dinka and the Nuer, the BBC reported.
UN Secretary-General Ban Ki-moon said he was "deeply concerned by reports of growing violence in many parts of South Sudan, human rights abuses and killings fuelled by ethnic tensions".
However, the government insisted the clashes were over power and politics, noting that both sides involved in the clashes include leaders from different tribes.
"We condemn in strongest possible terms attempts to depict the coup as ethnic strife," a government statement said.
The UN is sheltering more than 30,000 civilians in five state capitals, including Juba and Bor.
United States President Barack Obama also warned the country was on the precipice of civil war, and said military personnel had been deployed to protect US citizens and property.
US ambassador to South Sudan Susan Page said she had met the country's leaders to discuss ways to stop the violence.
"It has spread throughout the country and we are encouraging every possible means for a peaceful end to the violence and some sort of negotiations to stop the ethnic nature that some of the fighting has taken on," Ms Page said.