regional commissioner Goi Jooyul Yol told AFP.
He said 100 women and children, 50 men and 11 soldiers were among the dead.
"We have 161 confirmed dead, and people are searching in the bushes for more casualties," Yol said.
"We fear there may be more dead to find," he added. "The situation in Akobo town is tense, and those fleeing the fighting are continuing to arrive into the town," he added, speaking by telephone from Bor, the capital of Jonglei.
Yol said the fighting had ended but there were concerns that the violence might resume.
"People are hungry and the situation is serious," Yol said. "However we are still hoping that this will not escalate and that talks between all groups will be possible."
UN chief Ban Ki-moon condemned the fighting and called on local authorities to bring those responsible to justice.
"The Secretary General notes with extreme concern the August 2 attack in Akobo, Jonglei state, southern Sudan, and condemns the reported killing of 161 people, including 100 women and children," said a statement released by UN spokeswoman Michele Montas in New York.
Ban called on the government of southern Sudan to bring to justice those responsible for these events and take the necessary measures to protect civilians across south Sudan.
The latest fighting comes almost three months after 250 people were killed when Murele fighters attacked Lou Nuer villagers in the same region.
As many as 750 people were killed in clashes a month before in Pibor county further south.
In all, more than 1,000 people have died and many thousands more have been displaced by fighting in the south in recent months, with UN officials warning that the recent rate of violent deaths now surpasses those in Sudan's war-torn western region of Darfur.
Jonglei state was one of the areas hardest hit in Sudan's two-decade-long north-south civil war, which ended in 2005 with a power-sharing deal between the Muslim north and the Christian and animist south.
The state remains awash with small arms and there are frequent clashes between rival groups.
Heavy-handed but ineffective disarmament campaigns have left regions at risk of attack from their still armed neighbours.
Under the deal that ended Africa's longest civil war, the south has a six-year transitional period of regional autonomy and takes part in a unity government until the 2011 referendum on self-determination.
Authorities struggle to maintain order in the sprawling state, which is the size of Austria and Switzerland combined.
Forty soldiers were killed in June when an ethnic group attacked barges carrying food aid on the Sobat river.
The attacks followed clashes in May between factions of the Lou Nuer and Jikany ethnic groups, in which at least 66 people were killed according to local officials.
The fighting has raised fears of potential future instability with national elections due in February 2010.