Dramatic new allegations have been made about a massacre allegedly committed by pro-government forces in western Sudan.
Refugees fleeing Darfur have told horrific tales
New York-based group, Human Rights Watch says it has established that pro-government militias executed 136 men in a coordinated operation last month.
The allegation comes as the United Nations Human Rights Commission adopted a watered down statement on Darfur.
The United States had pushed for a much harder hitting resolution criticising Sudanese government abuses.
Unlike the original draft resolution, the text does not go into details about the targeting of civilians by the Arab militias in Sudan, or mention rape, sexual assault and forced removals of black communities in the area.
Rather than condemning Sudan, it expresses solidarity with the country in overcoming the present situation.
Critics say this is a considerable climb-down by the UN and the resolution was voted against by the US.
"We fear a terrible famine to come when tens of thousands may well perish," the US envoy Richard Williamson said. "The commission so far has failed to meet its responsibility today."
He said once a UN investigation team had submitted its report, he would ask delegates to reconvene in a special session to consider further action.
The UN says more than 10,000 people have been killed and over one million displaced over the past year as a result of conflict in Darfur.
HRW says last month, men from the Fur ethnic group were rounded up with the help of government forces, and delivered to their place of execution in army lorries.
The Sudanese government has not responded to the report.
Talks aimed at ending the fighting in neighbouring Chad are reported to be making little progress.
The BBC's Will Ross, in the Chadian capital, N'Djamena, said that on day four of the talks, the total time the opposing sides have spent in each others' company can still be counted in minutes.
The two rebel groups - the Sudanese Liberation Movement (SLM) and the Justice and Equality Movement (Jem) - accuse the government of consistently breaking a recently agreed ceasefire by bombing villages and backing an Arab militia in the area.
A UN mission was due to travel to Darfur on Friday to investigate allegations of atrocities there.
But the Jem claims the Sudanese government is trying to derail the peace talks so that the deployment of observers is delayed and the attacks can continue.
Sudanese minister Mohammed Yussef Abdullah, however, said he was "confirming that there is no single bombing or single air raid that has taken place".
The lack of urgency at the talks provides little hope of an imminent end to the rising humanitarian disaster, our correspondent says.
Human rights campaigners expressed outrage on Thursday that a leaked UN report strongly critical of the Sudanese government was withheld from the UN debate.
The report, seen by the BBC, details claims of rape, looting and killing of non-Arabs by militias with government help.
It says the atrocities in Darfur "may constitute war crimes and/or crimes against humanity".
It was compiled by a UN team of experts who visited Chad to speak to refugees from the conflict.
Sudan was accused of delaying the team's trip to Darfur to prevent evidence of atrocities coming under discussion.
Jemera Rone of Human Rights Watch told BBC News Online: "The Sudanese government is playing games with the international community, trying to delay the day of reckoning and prevent any systematic monitoring of its atrocities in Darfur."
The UN secretary general himself has talked of his sense of foreboding over the situation in Darfur, drawing parallels with the situation before the Rwandan genocide.