A spokesman for the South Sudan opposition on Monday accused government forces of harassing and sometimes killing civilians in Unity and Jonglei states.
"The government troops go out in Unity state... They hunt the ordinary people who are living in villages, people who are suffering because there are no services. They go out and hunt them, they go and kill people. The same thing in Jonglei state," the opposition's head of humanitarian affairs, Hussein Mar Nyuot, said.
Army spokesman Philip Aguer said the government has not had any complaints from civilians of harassment by the Sudan People's Liberation Army (SPLA).
Mar Nyuot's accusations came days after a rebel militia leader and a commander of the SPLA were sanctioned by the European Union for blocking the peace process and breaching the January ceasefire deal.
Mar Nyuot insisted that the opposition is committed to ending the seven-month conflict in South Sudan, and that its forces have not violated the cessation of hostilities agreement signed in January.
But, he said, "We will defend areas where we are because there are local people who live in the areas we control," who are being attacked by government forces.
Lucy Poni contributed to this report.