The government and rebels in South Sudan have accused each other of violating a ceasefire, hours after it came into effect.
A deal to end the five-month conflict was signed on Friday in Ethiopia and was meant to end five months of fighting which has left thousands dead and more than 1 million displaced.
The army said rebels attacked government positions in the early hours of Sunday in the town of Bentiu in Unity State, the BBC reports.
The rebels said their positions were targeted by ground attack and artillery in Unity and Upper Nile states.
At the signing ceremony in Addis Ababa, President Salva Kiir and rebel leader Riek Machar met face-to-face for the first time since hostilities broke out and agreed to halt fighting within 24 hours.
But in a statement rebel military spokesman Lul Ruai Koang said the reported violations showed "that Kiir is either insincere or not in control of his forces."
The army said the rebel attacks in Bentiu had been repelled.
The BBC reports no independent verification of either side's claims.
A previous deal, signed in January, collapsed in a matter of days, with each side accusing the other of breaching terms.
The United Nations has accused both the South Sudanese government and the rebels of crimes against humanity, including mass killings and gang rape.
The trouble began when President Kiir accused his sacked deputy Mr Machar of plotting a coup.
Mr Machar denied the accusation, but then marshalled a rebel army to fight the government.
The battle developed ethnic overtones, with Mr Machar relying heavily on fighters from his Nuer ethnic group and Mr Kiir from his Dinka community.
The UN has about 8500 peacekeepers in South Sudan.
South Sudan gained independence in 2011, breaking away from Sudan after decades of conflict between rebels and the Khartoum government