South Sudan's government and rebels traded accusations that each had breached a ceasefire deal by attacking the other, but insisted they were committed to ending weeks of brutal conflict.
Both sides insist they were attacked and have responded only in self-defence.
The ceasefire, aimed at stopping five weeks of bitter fighting in which thousands have died, began Friday evening with both sides reporting clashes as the deadline approached.
Up to 10,000 people are believed to have been killed in the fighting pitting forces loyal to President "Salva Kiir" against a loose coalition of army defectors and ethnic militia nominally headed by sacked vice president "Riek Machar", a seasoned guerrilla fighter.
Rebel military spokesman "Lul Ruai Koang" reported Sunday "clear violations" of the ceasefire, claiming government forces had attacked rebel positions in the northern oil state of Unity and in the volatile eastern Jonglei region.
He said in a statement "in all government's offensives, our forces only acted in self-defense".
The army has dismissed the reports, blaming the rebels for attacking their forces.
Both sides insist they are committed to the deal, and the clashes reported since the agreement was signed late Thursday appear to have been localised skirmishes, not large-scale assaults.
Verifying reports from across the vast and remote regions of South Sudan - large areas of which have poor if any telephone networks - is a difficult task.
But both sides have also said they doubt the other can fully control the forces on the ground.
Information Minister "Michael Makuei", speaking on Saturday in Juba after returning from the talks in Ethiopia that hammered out the crucial deal, said the clashes were not unexpected, as the "rebels are indisciplined".
Rebel spokesman Koang said government orders to soldiers not to kill civilians was a sign that Kiir was "not in full control of security forces" either.
The fighting has been marked by atrocities on both sides, with about 700,000 people forced from their homes in the impoverished nation, according to the United Nations.