US President Barack Obama on Monday said the situation in civil war-torn South Sudan was deteriorating but that it was now time for a "breakthrough" in peace efforts.

"Unfortunately, the situation continues to deteriorate. The humanitarian situation is worsening. The possibilities of renewed conflict in a region that has been torn by conflict for so long and has resulted in so many deaths needs addressing," Obama said in the Ethiopian capital Addis Ababa.

"We don't have a lot of time. The conditions on the ground are getting much much worse. The goal is to make sure the US and IGAD (a regional bloc leading the peace process) are aligned on a strategy going into this endgame on peace talks," Obama said.

"Now is time for a breakthrough."