Annan said he feared the UN was once again failing to fulfill its promise to "never again" stay silent in the face of war crimes.
"Sixty years after the liberation of the Nazi death camps, and 30 years after the Cambodian killing fields, the promise of 'never again' is ringing hollow," Annan said.
"How can an international community which claims to uphold human rights allow this horror to continue?" he said, referring to Darfur, where the UN cited "disturbing reports" of gross violations of human rights. "There is more than enough blame to go around."
Annan also blamed the continuing violence in Darfur on "those who value abstract notions of sovereignty more than the lives of real families, those whose reflex of solidarity puts them on the side of governments and not of peoples."
This was a clear reference to Khartoum's refusal to accept the deployment of 20,000 UN peacekeepers to replace the 7,000-member AU force currently operating in Darfur.
Last month, Sudanese President Omar al-Bashir agreed in principle to allow a "hybrid" AU-UN force, but he later reiterated his opposition to the deployment of UN troops in the war-torn region.
"International troops are a colonization of Sudan," al-Bashir recently told reporters.
Annan, whose term ends Dec. 31, warned that Khartoum's resistance to external help is "placing the government in a very difficult situation."
"In time they may have to answer collectively and individually for what is happening in Darfur," he said.
The outgoing UN chief also said that he is disappointed that the Human Rights Council, which replaced the discredited Human Rights Commission in June, had only recently agreed to discuss the Darfur conflict.
"I hope against hope that it will find an effective way to deal with this burning issue," he said.
Analysts criticize the international community for failing to resolve the crisis in Darfur, where more than 200,000 people have been killed and 2.5 million displaced by three years of fighting.
The Sudanese government, which accuses the rebels of starting the Darfur conflict, has always denied backing the Janjaweed militias, who are accused of committing the atrocities in the western Sudanese region.
The rebels, on the other hand, say that they are defending the "African" farmers against the government and the Janjaweed militia.