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

London-based Amnesty International and New York-based Human Rights Watch said Tuesday they have evidence that Sudanese forces have carried out an “indiscriminate bombing campaign” since June.

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.

Researchers said they witnessed nearly 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 have struck.

Amnesty International's Africa director, Erwin van der Borght, called on the United Nations to condemn the bombings and set up an independent investigation of abuses during the conflict in Southern Kordofan.

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

Sudan's government is engaged in heavy fighting with ethnic Nuba rebels, who are seen as supporters of South Sudan, which declared independence from the north in July. Nuba fighters sided with the south during Sudan's 21-year north-south civil war.

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.