A South Sudanese presidential spokesman says four people have been killed by an apparent Sudanese air strike on South Sudan's territory.

Ateny Wek Ateny said Thursday that nine more people were wounded in what he called "an act of aggression" by Sudan. He said Sudan is to blame because it is the only neighboring country with "the history of this type of unprovoked attacks."

Deng Kuel Kuel, the head of a local commission that coordinates emergency and humanitarian response in Northern Bahr al Ghazal state bordering Sudan, said two children were among those killed in an aerial bombing Wednesday.

South Sudan broke away from Sudan in 2011 following decades of armed struggle, though border skirmishes have continued.

Both countries at times trade accusations over harboring or supporting rebels.