Sudan has submitted a complaint about South Sudan to the U.N. Security Council, accusing the south of sparking unrest in a border state.

A spokesman for Sudan's foreign ministry said Tuesday that the complaint accuses South Sudan of supporting rebels in Sudan's Southern Kordofan state.

Sudan's government is battling ethnic Nuba fighters in the state, who are seen as supporters of South Sudan, which declared independence from the north in July.

Two human rights groups say Sudan's army may have committed war crimes in Southern Kordofan.

Amnesty International and Human Rights Watch said Tuesday they have evidence of an “indiscriminate bombing campaign” by Sudanese forces.

Also Tuesday, the United Nations says Sudan's government has denied aid groups access to Southern Kordofan, leaving many people in a life-threatening situation.

The U.N. Undersecretary-General for Humanitarian Affairs said Sudan's government has denied permission to international aid agencies to replenish their stocks for the past six weeks. She said unless aid groups are allowed immediate access, people in many parts of Southern Kordofan face potentially catastrophic levels of malnutrition and mortality.

Last week, Sudanese President Omar al-Bashir called for a two-week unilateral cease-fire in Southern Kordofan. The fighting near the Sudan-South Sudan border has forced tens of thousands of Nuba from their homes.

Nuba fighters supported the south during Sudan's 21-year north-south civil war.

Human rights groups said in their report Tuesday that their investigators witnessed almost daily bombings during a visit to the Nuba Mountains earlier this month, and that victims and witnesses said there were no military targets near where the bombs struck.

Previously, the U.N. said it received reports of indiscriminate killings, widespread looting and massive civilian displacement in Southern Kordofan. It blamed most of the violence on Sudan's army, police and allied militia.