Roughly a third of children in developing nations are forced to miss school because they must work, and the same number say their schools are unsafe, according to research released on Monday.

The highest rate of absenteeism among the 41 nations surveyed was in Afghanistan, where nine out of 10 children said work made them unable to go to school, said the ChildFund Alliance, a global network that promote children's rights.

Globally, some 59 million children do not attend primary school, according to UNICEF, the United Nations' children's agency.