The UN's top official in South Sudan on Saturday said "no evidence" had been found of reported mass killings, but warned that 60,000 people were in urgent need of aid.
Hilde Johnson, UN Special Representative for South Sudan, said reports that over 3,000 people were killed last week when thousands of armed youths attacked the Pibor region of Jonglei state appeared to be a false alarm.
"Importantly, we found no evidence that support those numbers," she said following a visit to affected areas where up to 8,000 rampaging armed youths set homes on fire and forced thousands to flee.
In a dramatic escalation of bitter tit-for-tat attacks, a militia army from the Lou Nuer tribe last week marched on Pibor, home to the rival Murle people, whom they blame for abductions and cattle raiding.
It was still not clear on Saturday how many people had died but with as many as a third of all thatch huts set on fire in targeted areas, some 60,000 people were in desperate need of help, Johnson added.
"People are left without shelter, their homes have been torched, and with their cattle taken their livelihoods are dismantled," she said.
"It is critical that this cycle of violence stop... and providing timely humanitarian assistance can help end retaliatory attacks."
The UN humanitarian coordinator for South Sudan, Lise Grande, said last week that "tens, perhaps hundreds" could have died in the latest outbreak of violence in the world's newest nation, which only declared independence six months ago.
Johnson stressed that UN peacekeepers had, however, protected civilians from the county's two largest settlements of, Pibor town and Lekongele.
"Our mandate is to protect civilians, and we did that," she added.
South Sudan has declared Jonglei a national "disaster area" while the United Nations has said it will launch a "massive" emergency operation to help those uprooted by the violence.
"This emergency operation is going to be one of the most complex and expensive in South Sudan," since the Sudan's civil war ended in 2005, the UN said earlier.