A United Nations agency says the number of children killed and injured in Afghanistan's war has risen sharply this year.

The U.N. Children's Fund says 414 children have been killed or injured in the first four months of this year, up 27 percent over the same period the previous year. The agency says this is "unacceptable" and "very worrying."

UNICEF said Thursday that 121 children were killed and 293 were injured this year, through April 30. Roadside bombs accounted for the largest number of casualties, with 37 percent.

Violence is increasing overall in Afghanistan as the Taliban and other militants press an intense offensive against government targets as international troops hand over security to Afghans. The international coalition is set to end its military mission by the end of 2014.