South Sudan’s main rebel group, SPLM-IO, has accused government forces of attacking their defensive positions after both sides signed a peace deal.
The United Nation mission also said one of its peacekeepers was shot and wounded by a government soldier.
President Salva Kiir had signed a peace deal with the main rebel leader, Riek Machar, in the Ethiopian capital last Wednesday, to end a civil war that has killed 50,000 people, and displaced about three million.
The war has truncated the country's progress since it gained independence from Sudan seven years ago.
“The regime’s forces heavily stormed our position at Mundu in Lainya county,” said Lam Paul Gabriel, the rebels’ deputy military spokesman, in a Statement.
Paul Gabriel revealed that the attack happened in the early hours of Friday, adding that eight government troops were killed in the ensuing battle.
Another attack reportedly occured in Mangalatore, near the site of the first attack, where four government soldiers were also killed, the statement further claimed.
Both Mundu and Mangalatore are in Yei River State, close to the border with Uganda.
The UN Mission in South Sudan, UNMISS, said one of its peacekeepers from Nepal was shot in the leg on Saturday in Yei, the state capital, by a government soldier.
The peacekeeper was said to have been wounded, when a soldier opened fire on a convoy of vehicles that left the U.N. base to fetch water in the town. UNMISS also stated that the peacekeepers could not return fire due to the presence of civilians in the area.
“This direct attack on UN peacekeepers here to help the people of South Sudan is unacceptable,” said David Shearer, the head of UNMISS. “The perpetrator must be found and held accountable by government authorities.”
Sudan and other neighbouring countries are said to fear that an escalation in the conflict could cause flood of refugees.
The civil war in South Sudan started in 2013, instigated by personal and ethnic rivalries.
According to the UN, one quarter of South Sudan’s 12 million population has been displaced, with its economy, which heavily relies on crude oil production, ruined.