Addis Ababa - South Sudan's warring sides have violated a ceasefire agreement over 50 times in the last 20 months, mediators said in a report on Thursday.
The world's newest nation plunged into civil war in late 2013 after a political row between President Salva Kiir and his former deputy Riek Machar reopened ethnic fault lines between Kiir's Dinka and Machar's Nuer people.
More than 10 000 people have died.
Facing heavy international pressure and the threat of sanctions, Kiir and Machar signed a peace deal in August.
But since then both sides have accused one another of attacks, and humanitarian groups have pulled out of parts of the oil-rich country where heavy violence has been reported.
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The East African bloc IGAD, which is mediating peace talks, said in its latest report rebels had committed 29 violations and government troops had committed 24 violations between February 2014 and last month.
IGAD's monitors said the latest violation, on September 22, occurred when rebels attacked and looted the government-held town of Guit in the northern Unity region "causing both military and civilian casualties" before their withdrawal.
"This incident demonstrates a complete disregard of the recently-signed permanent ceasefire by a group of SPLM/A-IO Forces in Unity State," IGAD said, referring to the rebels.
Machar's rebels rejected the accusation, claiming they were attacked first.
"In the process of pursuing [the attackers], our forces ended up capturing Guit, Leer and Koch but we withdrew from the said areas because we were not intent on capturing the places to violate the ceasefire," said William Gatjiath Deng, a rebel spokesperson.