The mission would interview refugees who had fled into neighbouring Chad to escape fighting between rebels and government forces as well as visit Darfur in western Sudan.
"Given the urgency of the situation, the Office of the High Commissioner (for Human Rights) hopes to deploy the mission in the coming days," said spokesman Jose Luis Diaz on Friday.
But he added that the Geneva-based UN human rights agency had yet to receive a reply from the Sudan government to its request to visit the area, where the UN estimates between 600,000 and 700,000 people have been driven from their homes.
The Khartoum government blames the violence on the Sudan Liberation Movement/Army (SLM/A) and the Justice and Equality Movement (JEM).
The groups launched a revolt in February last year accusing Khartoum of neglecting Darfur and arming Arab militias to burn and loot African villages.
Witnesses tell of executions, public hangings and mass rape campaigns in the poor and arid region, which is far from the oil fields of southern Sudan, where a civil war, with another rebel group, raged for 20 years until a recent truce.
More than 600,000 people have
fled the conflict-stricken west
"One can talk of a situation that is equivalent to ethnic cleansing," Daniel Augstberger, a UN emergency relief coordinator, said on Thursday on his return from the area.
US human rights group Human Rights Watch, in a report also released on Thursday, accused government armed forces of indiscriminate bombing of civilians.
It said that troops and militia were destroying villages of the ethnic Fur, Masaalit and Zaghawa peoples.
The US and the European Union are seeking to mediate talks between the government and rebels in the Chadian capital, N'Djamena.
But the JEM rebel group said on Friday it planned to withdraw from peace talks with the government.
JEM said Chadian authorities had declined to grant its political delegation entry visas to join the talks in the Chadian capital N'Djamena.
"This withdrawal will be effective from... Monday 5 April," said the statement, signed by JEM spokesman Idris Ibrahim Azraq.