The new pupils at Kiriani boys' high school in Eastern Province had only been at the school for three days.

The pupils were told not to return until they had completed the procedure.

"Please do the needful within two weeks and let your son report back to school with you immediately he is well," a letter to parents from the school said.

Circumcision is not obligatory for admission to secondary school, but a study released in December said it reduced the risk of contracting HIV/Aids.

Circumcision is practised in many, but not all, of Kenya's various ethnic groups.