The World Food Programme (WFP) says it is rapidly boosting its support on the Chad-Sudan border to deal with thousands of people fleeing fighting between Sudanese military factions.
The UN agency says about a 250,000 people have fled to Chad since the conflict began in April.
In the last week alone, 20,000 have crossed from the Darfur region to the Chadian border town of Adré.
The WFP says many are arriving seriously wounded.
There are reports that fleeing civilians are being deliberately targeted, with an increasingly ethnic dimension to the violence.
Earlier, the campaign group, Human Rights Watch, called on the International Criminal Court to investigate war crimes committed in the western Sudanese region of Darfur, including the killings of dozens of civilians.