South Sudan's government forces and largest rebel group clashed in the north of the country, with each side accusing the other on Monday of instigating the fighting, which comes just two weeks after they signed a peace deal.
It was unclear if there were any casualties.
President Salva Kiir signed a peace agreement with rebel factions to end a civil war that has killed at least 50,000 people, displaced 2 million and limited the country's development since it gained independence seven years ago.
Lam Tungwar, state Minister of Information in Liech state, formerly part of Unity State, said fighters belonging to the main rebel SPLM-IO force loyal to former vice president Riek Machar had attacked government positions in a small village in Koch County.
He said the attack occurred while the government was carrying out exercises aimed at integrating various fighters with the army in the areas under their control.
"They were attacked by the forces loyal to Riek Machar," Tungwar told Reuters. "We are still receiving details of casualties if there were any."
Machar's SPLM-IO in turn said government troops had attacked their positions in the same region on Monday afternoon.
"They made a coordinated attack on our defensive positions of Mirmir, Ngony and Koch. The architect of this attack is Gen. Peter Dor Manjur and the pro-government militias that they mobilised recently," SPLM-IO deputy military spokesman Lam Paul Gabriel said, adding that the fighting was still going on.
South Sudan plunged into warfare two years after independence from Sudan in 2011 when a political dispute between Kiir and Machar erupted into armed confrontation.
A previous peace deal signed in 2015 fell apart a year later after clashes broke out between government forces and rebels.
Machar and other insurgent factions signed the latest agreement with the Juba government after assurances that a power-sharing accord would be honoured. The deal, mediated by Sudan, reinstates Machar to his former role as vice-president.