The US ambassador to the UN has accused Sudan of intensifying attacks on civilians and of deliberately bombing schools and hospitals.
Samantha Power condemned the attacks in the southern states of South Kordofan and Blue Nile, which she said were being carried out by the Sudanese government and its support forces against ordinary people.
Ground and air attacks have increased since April, with hundreds of barrel bombs and other explosives dropped on towns and villages, deliberately targeting hospitals and schools, she said.
Power also condemned on Thursday the alleged targeting of civilian aid workers, which she said would seriously violate international law if proven accurate, the AFP news agency reported.
Ethnic minority rebels in the area have been fighting government forces for three years, in a conflict which the UN says has affected more than one million people.
Unrest has been fuelled by grievances among non-Arab groups over neglect and discrimination by the Arab-dominated government in Khartoum.
Power warned the conflict had "increased the population's vulnerability to disease and malnutrition; and it has disrupted planting cycles, which will only compound food insecurity in the regions".
She 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.
The US has called on all armed groups in Sudan to stop violence against civilians and to comply with international law.