"This is a violation of the cessation of hostilities agreement, and we will act in self defence," the country's defense minister told AFP.
A ceasefire, the seventh in the conflict, was signed on February 1, and plans were made to begin negotiations by March fifth.
On Monday, the United Nations launched a $1.8 billion aid initiative after announcing that almost a quarter of the country's 11 million population is on the brink of famine and half of the population needs aid.
The Dinka and Neur tribes warred against each other in other in Sudan's civil war during the early 1990s, and the current conflict is also being fought predominantly among tribal lines. Monday's agreement is the latest of numerous attempts to end the fighting. A ceasefire deal agreed to in November was broken within hours, and a western diplomat told AFP that the current deal “is not a significant breakthrough, this is a small step at the most."
South Sudan became an independent state in 2011 after voting in a referendum for independence from Sudan. The secession came after five decades of conflict in Sudan since the country gained independence from British colonial rule in 1956.
