South Sudan's army repelled a fresh rebel attack on Monday, the latest battle to rock the country despite a ceasefire aimed at ending a brutal 21-month civil war.
Army spokesman Philip Aguer said rebels attacked government positions close to the key town of Malakal -- capital of Upper Nile state -- early Monday, but the army "repulsed them, and the situation was now calm."
But he also said that large numbers of militia fighters, from the ethnic Nuer "White Army" force, were "massing south of Malakal preparing for an attack".
The army and rebels have repeatedly accused each other of breaking an August 29 ceasefire deal, the eighth such agreement to have been signed since war broke out in December 2013. Despite ongoing fighting, both sides say the political deal remains in place.
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On Sunday, Aguer said rebels and the army had fought in the neighbouring battleground state of Unity, leaving five soldiers and a woman dead as well as several injured.
"There too the situation is now under control," Aguer said.
It was not possible to independently verify the reports. Each side has previously dismissed the other's accusations as lies.
The world's youngest nation, independent since July 2011, South Sudan descended into bloodshed in December 2013 when President Salva Kiir accused rebel chief Riek Machar, his former deputy, of planning a coup.
The violence has left tens of thousands dead and the poverty-stricken country split along ethnic lines.
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Over two million people have fled their homes from a war marked by ethnic killings, gang rapes and the forced recruitment of child soldiers.
Some 190,000 terrified civilians are sheltering inside UN bases.
Monitors from the regional East Africa bloc IGAD, which led efforts to negotiate the peace deal, are meant to be overseeing the ceasefire.
But IGAD personnel lack the resources to monitor the rival forces, fractured into multiple militia units, with the rebels themselves divided.