South Sudan says Sudan has carried out cross-border airstrikes in violation of a United Nations-backed cease-fire.

Military spokesman Kella Dual Kueth on Wednesday accused Sudan of bombing and shelling sites in four northern states — Unity, Upper Nile, Western Bahr el Ghazal and Northern Bahr el Ghazal.

A commissioner in Western Bahr e Ghazal, Riziq Dominic, told VOA the air strikes began Monday and continued Tuesday and Wednesday.

“When the other plane finish dropping their load, the other one come and drop. I think there are around three planes. Even today I am talking to you they are still dropping.

Last week, the U.N. Security Council passed a resolution that called on the two Sudans to cease hostilities by Saturday or face possible sanctions.

The neighboring countries have accepted “in principle” an African Union roadmap for an end to the fighting. The deal calls for the Sudans to settle their disputes in 90 days or face binding international arbitration.

Rising tensions have pushed the countries to the brink of war, just 10 months after South Sudan formally split from the north.

The countries have yet to resolve critical issues from their split, including citizenship questions and disputes over oil revenue and borders.

The fighting has displaced tens of thousands of people along the two countries' border area, creating a humanitarian crisis that aid agencies say is rapidly growing worse.