The UN Security Council has said the Sudanese government must honour its pledge to disarm Arab militias, blamed for violence in the Darfur region.
More than a million Sudanese have been forced from their homes
In a unanimous statement, the council warned of "a stark and mounting crisis" and urged the government to co-operate fully in the humanitarian effort.
Aid officials have said bureaucratic delays have restricted access to those displaced from the western region.
Some one million people have fled since the conflict began in February 2003.
Pro-government militias are accused of "ethnic cleansing".
Black Africans in the region say the Arab "Janjaweed" militias are chasing them from their homes and are working with government forces.
Some 130,000 people have fled to neighbouring Chad, while an estimated 900,000 are displaced within Sudan.
UN officials have said the conflict is now the worst humanitarian crisis in the world.
However, the security council has previously rejected calls to intervene in the Darfur conflict.
The 15-nation council expressed concern about reports of "indiscriminate attacks on civilians, sexual violence, forced displacement and acts of violence, especially those with an ethnic dimension".
The statement demanded "that those responsible be held accountable".
The council also called for the immediate deployment of international monitors to Darfur and urged the Sudanese government and opposition groups to ease their efforts, the Associated Press reported.
The statement is not legally binding, but it carries moral
weight - and puts new pressure on Sudan to end the violence, correspondents say.
"This is a chance for Sudan to become part of the
solution instead of being part of the problem," said US
envoy Stuart Holliday, in remarks quoted by the Associated Press.