The United States has accused Sudan of stepping up its attacks on civilians in South Kordofan and Blue Nile states.
Samantha Power, the American ambassador to the UN, condemned the attacks in which she said schools and hospital had been deliberately targeted.
Ms Power said since April Sudanese aircraft had dropped hundreds of barrel bombs on towns and villages.
More than a million people are reported to have been displaced by fighting between government forces and rebels.
Sudan’s ambassador to the UN did not respond to the comments.
Earlier this week aid agencies wrote to the UN Security Council, African Union and the Arab League demanding an end to attacks on civilians by the Sudanese government.
Ms Power condemned “in the strongest possible terms” the Sudanese government’s offensive in the region.
Ground and air attacks have increased since April and many have targeted civilian aid workers, which if accurate would seriously violate international law, she said.
Ethnic minority rebels in the area have been fighting government forces for three years in a war that the United Nations says has affected more than one million people.
Unrest has been fuelled by grievances among non-Arab groups over what they see as neglect and discrimination by the Arab-dominated government in Khartoum.
Ms Power compared the government’s tactics with those used in the war-torn western region of Darfur, where more than 300,000 people have been displaced so far this year alone, she said.
“The US calls on all armed groups in Sudan to cease all violence against civilians and comply with international law,” she said.