Juba - Fighting resumed in South Sudan after rebel forces attacked the capital of the oil-producing state of Upper Nile, a military official said on Tuesday.
Fighting broke out early on Tuesday in Malakal, which once was in rebel hands but is now controlled by government troops, said South Sudanese military spokesperson Colonel Philip Aguer.
"We were expecting it because the rebel commander in the area said he would not respect a ceasefire," he said.
Although the country's warring factions signed a ceasefire on 23 January, both sides have repeatedly accused each other of violating that agreement. The international community has repeatedly urged both sides to respect the ceasefire.
Toby Lanzer, the United Nation's top humanitarian official in South Sudan, said on Twitter on Tuesday that all groups "engaged in the violence must uphold people's rights and protect non-combatants."
The UN says both sides have committed rights violations, and on Monday South Sudan's military announced more than 20 government soldiers had been charged over civilian killings.
Thousands of people have been killed and more than 800 000 displaced by violence since mid-December, when a fight broke out among presidential guards in the capital, Juba, before spreading out across the country.
Ugandan forces are fighting alongside the South Sudanese military as it tries to put down a rebellion led by former Vice President Riek Machar, an influential politician whose dismissal last year sparked ethnic tension in a country with a history of divided military loyalties.
Machar is Nuer, the ethnic group of most of the soldiers who defected and joined his rebellion late last year. Most of the loyalist forces are from the Dinka ethnic group of President Salva Kiir, whose government insists that unrest in the country was sparked by a failed military coup mounted by soldiers loyal to Machar.
Machar denies the coup allegation but says his goal is to have Kiir removed from power.