Five Indian peacekeepers and at least seven UN civilian workers were killed on Tuesday in an ambush in South Sudan with others still missing, officials said, a day after warnings about spiralling violence.
Hilde Johnson, the top UN official in South Sudan, "condemns the strongest terms the killing today of five peacekeepers and seven civilians working with UNMISS (United Nations Mission in South Sudan) in an ambush by unidentified assailants", she said in a statement.
"At least nine additional peacekeepers and civilians were injured in the attack, and some remain unaccounted for," she added.
Indian foreign ministry spokesman Syed Akbaruddin blamed unknown "rebels" who attacked while the soldiers were "escorting a UN convoy".
The volatile eastern state of Jonglei has been the scene of widespread ethnic conflict since South Sudan became independent in July 2011, with bloody battles between rival tribes, including the Dinka, Lou Nuer and Murle people.
Clashes between the army and a former theology scholar turned rebel called David Yau Yau from the Murle people have devastated large parts of this troubled region.
Still reeling from more than two decades of civil war that left this region awash with guns and riven by ethnic hatred, traditional cattle raiding between rival tribes has escalated into a wave of brutal killings.
South Sudan army spokesman Philip Aguer blamed Yau Yau for the attack, which took place close to an army base near Gumuruk, a remote village in the restive Pibor region.
Amid renewed clashes between ethnic groups and government forces, UN troops have recently stepped up their patrols to deter violence and fulfil their mission of protecting civilians.
An Indian soldier was shot and wounded in Jonglei in March amid high tensions about an imminent government crackdown on rebels, while the army shot down a UN helicopter in December by mistake, killing all four Russians on board.
Johnson warned Monday about the "destabilisation" of the region.
"Without stability and peace in Jonglei, the largest state in South Sudan, in the long run stability also in the country could be at risk," she told reporters.
"I urge the Murle, Lou Nuer and Dinka communities, their leaders, and the governments of Jonglei and South Sudan to resume and sincerely engage in peace initiatives," she added.
South Sudan's army launched the latest offensive against Yau Yau's rebels in March.
At the end of 2011, barely six months after South Sudan declared independence after decades of civil war with the north, some 8,000 armed Lou Nuer youths rampaged through Pibor County, vowing to exterminate their cattle-keeping rivals, the Murle.
The UN estimated that over 600 people were killed and around 300 in smaller revenge attacks.
A subsequent disarmament campaign led by security forces, mired in claims from rights groups of abuses against civilians, pushed some residents towards Yau Yau's militia.
India is a major contributor to UN peacekeeping forces around the world and has suffered losses in the past.
In 2010, rebels hacked to death three Indians in their camp in the Democratic Republic of Congo.
Akbaruddin said that the Indian foreign ministry was arranging for the bodies of its peacekeepers in South Sudan to be returned home.