South Sudan's rebels have accused government forces of multiple ceasefire violations along several fronts, just hours after a truce aimed at ending a five-month conflict in the world's youngest country came into effect.
Lul Ruai Koang, the spokesman of the rebels, said on Sunday the alleged violations happened in the oil-rich northern states of Upper Nile and Unity, and included both ground attacks and artillery barrages.
He added that rebels reserved "the right to fight in self-defence", the AFP news agency reported.
"The violations of the Agreement to Resolve the Crisis in South Sudan shows that [President Salva] Kiir is either insincere or not in control of his forces," Koang said in a statement.
Clashes were also reported around the northern oil hub of Bentiu - which has changed hands several times in recent weeks and has been described as being particularly tense.
In the capital Juba, however, the government said its troops had been given strict orders to respect the peace deal.
President Kiir's spokesman, Ateny Wek, told AFP: "The orders have been given to the army to start observing arrangements for the cessation of hostilities."
Kiir and former vice president and rebel leader Riek Machar met in the Ethiopian capital Addis Ababa on Friday and agreed to halt fighting within 24 hours - or by Saturday evening.
The agreement came after massive international pressure on both sides to stop the five-month conflict marked by widespread human rights abuses, a major humanitarian crisis and fears the country was on the brink of a genocide and Africa's worst famine since the 1980s.
The war - which began last December after the government foiled what it called a coup by Machar - has claimed thousands of lives, with more than 1.2 million people forced to flee their homes.
The conflict has also sucked in neighbouring Uganda, which has a large number of people working in the capital Juba, and sent troops in December to South Sudan to fight along side government forces.
Violence has taken on ethnic undertones, with rebels loyal to Machar's Nuer tribe and soldiers from Kiir's ethnic group, the Dinka, engaging in revenge killings.
Kiir and Machar had agreed to a ceasefire in January, but that deal quickly fell apart.