Officials in Jonglei state on Tuesday accused rebels loyal to former vice president Riek Machar of again violating the January 23 cessation of hostilities agreement by attacking SPLA positions in Ayod County.
State Information Minister Judi Jonglei Boyoris said many civilians fled as the SPLA fought and pursued the rebels.
But opposition military spokesman Lul Ruai Koang blamed the fresh outbreak of violence on government forces, who he said had attacked rebel positions in Ayod County.
"The government forces in the last two days have been shelling our positions at Kwei and Paloy. After shelling was halted, they made an advance on our positions and we fought them back and today we drove them back up to Ayod," he said.
Neither the government nor the opposition was able to give any casualty figures from the fighting, which came just a day after clashes in Nasir in oil-rich Upper Nile state.
US condemns fresh fighting
On Monday, the United States joined a chorus of condemnation of the new outbreak of fighting in Nasir. It blamed the clashes on opposition fighters.
"We call on both parties to immediately end all such attacks and fully adhere to their May 9 and June 10 commitments to cease hostilities and begin the disengagement of forces," U.S. State Department deputy spokeswoman Marie Harf said in a statement.
Harf called for an end to the fighting, which she said has caused "widespread displacement and a worsening humanitarian crisis as civilians fear returning to their homes."
She warned that famine could hit parts of South Sudan as of next month and urged both parties to "immediately recommit themselves to inclusive, political negotiations."
Peace talks for South Sudan were put on indefinite hold last month.