At least two hundred thousand people dead and two and a half million forced into refugee camps. That's the estimated human cost of the crisis in Sudan's Darfur region. Now the violence has dragged in neighbouring Chad. The UN said up to 400 people have been killed in Chad during cross-border raids by Sudanese Janjaweed fighters responsible for much of the violence in Darfur. And Chad has now admitted entering Sudanese territory and killing several soldiers. Darfur has been in a state of turmoil for nearly four years, but in the past 18 months the conflict has spread across the border into Chad.