She was speaking during a trip to a camp for displaced people outside the North Darfur state capital El Fasher.
"The United Nations estimates at 300,000 people the number of people who have fled fighting in Darfur in the first five months of the year," Amos said, according to an Arabic translation of her remarks.
In April the United Nations said 50,000 people from southwestern Darfur had fled to neighbouring Chad in the face of fighting between two feuding Arab tribes -- the Misseriya and Salamat.