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.
Researchers said they 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.
The groups said in a statement they have documented bombings in the towns of Kauda, Delami and Kurchi that have killed at least 26 people and wounded more than 45 others.
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.
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.