The United States on Friday called on Sudan to halt aerial bombing raids in Darfur and for UN sanctions experts to be allowed to carry out wider investigations in the country.
International concern over Sudan is growing as worsening conflict in the country's South Kordofan and Blue Nile states adds to the decade-old war with rebels in the Darfur region and growing tensions with neighbouring South Sudan.
The United Nations has repeatedly complained about lack of access to conflict zones in Darfur, where it says it has been prevented from reaching areas where government air attacks have been reported.
The United States is "profoundly concerned" by clashes between tribal militias in North Darfur and between the Sudanese army and rebels in the Jebel Marra district, said US State Department spokeswoman Victoria Nuland.
The renewed fighting has forced tens of thousands to flee their homes. Nuland said more people have been displaced in Darfur in the past month than in all of 2012.
Nuland said the United States urged Sudan to "urgently disarm militias" in Darfur, "to cease aerial bombardments" and implement a Darfur peace accord made with some rebel groups.
The past 10 years of conflict between Darfur rebels and the Arab-dominated Khartoum government has left at least 300,000 dead, according to the United Nations.
The United States is also seeking to increase pressure on the Sudan government through UN sanctions investigators.
The UN Security Council is due to renew the mandate of UN sanctions experts for Sudan on Wednesday. The current UN mandate allows them to investigate breaches of a Darfur arms embargo imposed in 2004.
Diplomats said the United States wanted to add language to the resolution to be passed Wednesday that would "threaten" to extend the experts' mandate to South Kordofan and Blue Nile, where the government has been battling rebels for the past two years.
Russia has opposed the move in talks, diplomats told AFP on condition of anonymity.
Humanitarian workers have highlighted how the 900,000 people who have fled Kordofan and Blue Nile is higher than the Syrian war refugee figure.
The Sudan government reached an accord with the United Nations and the African Union to grant humanitarian access to rebel-held zones, but has still kept aid workers out.
The Security Council "cannot tolerate ongoing impunity and should expand" the mandate of the Sudan panel of UN experts "to expose the crisis" in Kordofan and Blue Nile, Susan Rice, US ambassador to the United Nations, said on her Twitter account.
Rice added in another Twitter statement that she believed Sudan and South Sudan were at a "crisis point" because of the Khartoum government's refusal to implement an accord to end disputes with the rival neighbour.
South Sudan achieved independence from Khartoum in 2011 after a murderous two-decade civil war and a self-determination referendum.
The two sides still have disputes over territory and sharing revenues from oil reserves that are mainly on the southern side of the border but must be transported through the north.