As violence in Darfur escalates, a debate is growing over how many people have died in what officials call the world's worst humanitarian crisis. A U.N. agency's survey cites at least 200,000 deaths, but other studies say the death toll could be more than 400,000.
Sudan's government, however, contends the deaths are only a tiny fraction of that.
The dispute occurs in part because, since fighting began in early 2003, humanitarian workers have had only limited and perilous access to Darfur, an arid region of western Sudan nearly the size of Texas.
Both violence and government restrictions have kept aid groups and researchers away. Violence makes nearly 40 percent of the population inaccessible to aid workers, said Ramesh Rajasingham of the United Nations.
"To this day, we don't really have our eyes on the ground. We work with projections," Rajasingham said.
The U.N. says 4-million people in Darfur are in desperate need of aid - nearly two-thirds of the estimated population of 6.5-million. An estimated 2.5-million live in refugee camps in Darfur and neighboring Chad, while others inhabit remote villages, the U.N. says.
The last official, independent mortality survey for Darfur was published in March 2005. Based on data collected in refugee camps in Darfur, a team from the World Health Organization estimated that 10,000 of these refugees died each month between the end of 2003 and October 2004 - mostly of malnutrition and disease linked to the violence. By March 2005, the number had risen to 200,000, the WHO estimated.
The figures have not been thoroughly updated since. Yet fighting has worsened in the past few months.
That has led some researchers to contend that the estimate of 200,000 killed since 2003 is low. They say the violence has continued at the same or greater level each month since March 2005, meaning total deaths now could be more than 400,000.
For its part, Sudan's government in Khartoum says death tolls have been vastly inflated.
Sudanese President Omar al-Bashir said in September that only 10,000 people had died because of violence in Darfur since 2003. This week he lowered his figure to 9,000. "I challenge anybody to prove differently," Bashir said.
But academics who study the Darfur crisis put little stock in Khartoum's estimate. They say the exact extent of Darfur's killing cannot be proved because no research has been permitted on the ground by the government since March 2005.