Updated

The U.N. secretary-general says he is "alarmed" to hear that rockets were placed in a U.N.-run school in Gaza and that "subsequently these have gone missing."

A statement Wednesday by the spokesman for Ban Ki-moon expresses the U.N. chief's "outrage" at the incident.

"Those responsible are turning schools into potential military targets, and endangering the lives of innocent children," the statement says.

The statement demands that militant groups stop such actions and should be held accountable for endangering civilians.

No details on the number or kind of rockets are given. The location of the school is not given.

The statement also says Ban has asked for the immediate development of a plan to safely handle any weapons found on U.N. premises.