The warring sides in South Sudan accused each other of launching attacks that killed 18 civilians and violated the latest peace deal aimed at ending the nearly five-year-old conflict.
Lul Ruai Koang, spokesman for the government military SPLA said rebels attacked Maban in Upper Nile state in the far northeast near the border with Sudan on Sunday.
Government forces responded and in the battle rebels killed 18 civilians and wounded 44, he said. The dead included three Ethiopians and two Sudanese.
"The area is tense and the bodies have been buried," he said. "People have not yet gone back to their homes. The area is deserted."
Lam Paul Gabriel, deputy spokesman for the opposition SPLA-IO said their forces had been "heavily bombarded" by the military in the Maban area on Sunday and denied attacking civilians, saying: "It is not the policy of SPLM-IO to attack civilians."
South Sudan was plunged into war in 2013 after a political disagreement between President Salva Kiir and his former vice President Riek Machar exploded into a military confrontation.
The fighting has uprooted about a quarter of the country's 12 million population, slashed oil production and ruined the economy.
A peace pact last week that included a ceasefire that took effect on Saturday was the second attempt by regional mediators to try to end the war after a deal in 2015 failed.