South Sudan’s army and rebel forces blamed each other Sunday for violating a cease-fire hours after it came into effect, fighting that is sure to frustrate international mediators who had pressured both sides to halt the violence.

A U.N. official confirmed fighting around the flashpoint town of Bentiu, saying both sides fired shots. The army and the rebels also reported clashes elsewhere.

President Salva Kiir and rebel commander Riek Machar met Friday to sign the cease-fire deal, the second time that the two sides have promised to stop fighting after a January accord swiftly collapsed.

All fighting was supposed to stop 24 hours after the signing of the deal late Friday.

Philip Aguer, a spokesman for the South Sudanese army, said troops had been attacked in two positions in oil-producing Unity state, one of them near Bentiu, where an ethnically driven massacre last month raised fears of a potential genocide.

“They attacked only six hours after the cease-fire came into effect,” Aguer said, though he added that the government was able to repulse both assaults.

The U.N. official, who asked not to be named until more information was gathered, said that there was heavy fighting around Bentiu on Sunday morning but that it later became more sporadic.

Rebel military spokesman Lul Ruai Koang, meanwhile, blamed the government, saying its forces launched attacks in Unity state and Upper Nile state, another oil-producing region. He said shelling on rebel positions in Upper Nile began a few hours before the cease-fire deadline and continued into Sunday morning.

“The latest violations of the agreement to resolve the crisis in South Sudan shows that Kiir is either insincere or not in control of his forces,” the spokesman said.

Violence erupted in South Sudan in December after months of tensions sparked by Kiir’s decision in July to fire Machar, a longtime rival, from the post of deputy president.

The conflict threatens to tear apart a nation that gained independence from Sudan in 2011. Deep ethnic divisions are partly to blame for the violence, which pits Kiir’s Dinka people against Machar’s Nuer community.

The United States and the European Union had welcomed Friday’s agreement. Western powers were instrumental in South Sudan gaining independence.

Washington, which has slapped sanctions on commanders from each side, warned of further steps if fighting continued. The E.U. also said it was considering punitive measures against those who committed rights abuses or blocked talks.

— Reuters