KHARTOUM: Sudanese government forces are killing civilians in rebel-held border areas with indiscriminate bombardments that include improvised "barrel bombs" filled with nails and jagged metal, Human Rights Watch said on Wednesday.
A senior member of the Arab-African country's ruling party dismissed the report as "completely incorrect".
Rebellion broke out in the South Kordofan state in June last year - just before South Sudan seceded under a 2005 peace deal that ended decades of civil war between the north and south - and spread to Blue Nile state in October.
Hundreds of thousands of people have since fled their homes in the two states.
In its report, New York-based Human Rights Watch accused government forces of abuses including indiscriminate bombardment and shelling that has killed and injured scores of civilians.
"Government forces have raided villages, burned and looted civilian property, arbitrarily detained people, and assaulted and raped women and girls," it said in the report based on five trips to rebel-held areas of Sudan and refugee camps in South Sudan.
Sudan had dropped unguided bombs from Antonov cargo planes and high-flying jets, it said, adding researchers found evidence "barrel bombs" - crude, improvised devices filled with nails and other metal - had been used in Blue Nile state.
Ground forces and militias, including the paramilitary Popular Defence Forces, had attacked villages without distinguishing between civilians and combatants, it said.
The insurgents in South Kordofan and Blue Nile, known as the SPLM-North, fought as part of the southern rebel army during the civil war, but partition left them in Sudan.
They say they are fighting to protect ethnic minorities from repression while Khartoum accuses them of spreading chaos with the backing of their old comrades in South Sudan.
Rabie Abdelati, a prominent member of the ruling National Congress Party, dismissed the report as false and biased toward the rebels.
It was the insurgents, not Sudan's army, who were committing abuses and targeting civilians, he said, pointing to times the SPLM-North had shelled South Kordofan's state capital Kadugli.
"The SPLM northern sector is not targeting the military, they are targeting civilians," he said. "That is why I think this report is completely incorrect."
Human Rights Watch said it had heard reports of violations by rebels such as indiscriminate shelling but was unable to access government-held areas to confirm them.
Hundreds of thousands of people have fled their homes in the two states since the fighting broke out, more than 200,000 of them to neighbouring Ethiopia and South Sudan, the United Nations and aid agencies estimate.
Human Rights Watch said civilians were still threatened in the camps by the presence of soldiers from "various armies", and that women and girls spoke of the threat of sexual violence.
Sudan's restrictions on movement and independent humanitarian aid were "effectively blockading" rebel-held areas, where many people were hiding in hills and caves, surviving on dwindling food stocks with little or no access to clean water and medicine, it said.
In August, Sudan said it had agreed to an African Union-brokered plan to allow aid into rebel-controlled territory in the two states, but the deal was never implemented and Sudan now says it is expired.
Sudanese officials including President Omar Hassan al-Bashir are wanted by the International Criminal Court on charges of war crimes in Darfur, which they dismiss as inventions of hostile Western forces.