South Sudanese army and opposition officials accused each other of violating a ceasefire agreement signed six months ago as fresh fighting broke out Friday in the two oil-producing states of Unity and Upper Nile.
Army spokesman Philip Aguer said government forces were still "committed to the ceasefire" but were forced to retaliate after coming under attack in Unity state.
He said the Sudan People's Liberation Army (SPLA) was continuing to monitor opposition forces, who were reportedly moving closer to the town of Ayod, in preparation for another attack.
Aguer also said militia groups are crossing into South Sudan from Sudan to join the rebel forces in Unity and Upper Nile states.
"SPLA will continue monitoring them. We will never move out of our bases but we will teach them lessons while they continue to attack SPLA," Aguer said.
Opposition accuses SPLA
Opposition military spokesperson, Lul Ruai Koang, said the SPLA started the fighting by attacking rebel bases in Unity and Upper Nile states.
"Today in the morning, some government troops in two locations in Unity state, went to Guet County, east of Bentiu town," Koang said.
"They left their vehicles on the main road, went on foot to the nearby villages and started attacking our positions. They did the same in a place called Parkuil, in Mayom County. The government is entirely responsible for those attacks... they launched unprovoked attacks on our positions," he said.
The fresh fighting came as the European Union imposed sanctions on rebel militia leader Peter Gadet and SPLA commander Santino Deng. Both men led forces involved in fighting in Bentiu, the capital of Unity state, months after the warring sides signed a cessation of hostilities agreement in January.
The EU warned that it will impose more sanctions on South Sudanese officials if the two sides do not resume peace talks soon and make a real effort to end seven months of fighting.