More than 200,000 people have died in Sudan's Darfur conflict, according to a new scientific study.
The toll includes refugees who die of hunger and disease
US researchers writing in the peer-reviewed journal Science say that their figures are the most compelling and persuasive estimate to date.
An accurate count is hugely difficult in practice but hugely important in political terms, correspondents say.
On Thursday, Oscar-winning actor George Clooney urged the UN Security Council to stop the "genocide" in Darfur.
The UN says violence and displacement have recently increased in Darfur, despite a May peace deal.
Sudan has rejected a UN resolution authorising a 20,000-strong force for Darfur, saying it is an attack on its sovereignty.
Apart from the dead, more than 2m people have been driven from their homes in three years of fighting.
Sudan's government and the pro-government Arab militias are accused of war crimes against the region's black African population.
'No fewer than 200,000'
Unlike a natural disaster there is no simple way of counting the bodies in a war-torn environment, BBC science reporter Matt McGrath notes.
So international organisations and aid agencies have had to rely on surveys carried out on the displaced millions to try and work out how many have died.
These surveys have varied enormously, ranging from fewer than 70,000 to more than 300,000 deaths.
BBC science reporter Matt McGrath says that politically, accurate figures are crucial in determining whether the deaths in Darfur are genocide or - as the Sudanese government says - an exaggeration.
Dr John Hagan of America's Northwestern University believes his figures are the most credible estimate to date.
"We've tried to find a way of working between those overestimations and underestimations," he told the BBC.
"We believe the procedures we have used have allowed us to come to very conservative and cautious conclusions which we used to try to identify a floor to these estimates - a floor figure of 200,000.
"We do not believe it is possible or defensible to go below in estimating the scale of this genocide."
He and his colleague believe the eventual death toll may be much higher .
They have made no distinction between those dying as a result of violence and those dying as a result of starvation or disease in refugee camps.
Holocaust survivor call
In his impassioned speech, Mr Clooney told Security Council members genocide was taking place on their "watch", and how they responded would be their legacy.
Mr Clooney and his journalist father, Nick, spent five days in Darfur in April hearing personal stories of some of the victims of the fighting, and have campaigned on it since.
George Clooney has been a regular campaigner on Darfur
"It is the first genocide of the 21st Century and if it continues unchecked, it will not be the last," he said.
He was speaking at a special informal session hosted by US ambassador to the UN John Bolton.
Nobel laureate and Holocaust survivor Elie Wiesel, whose Foundation for Humanity organised the session, also addressed the council.
"You are the last political recourse of Darfur victims and you can stop it," he said.