Pakistani police have arrested a 17-year-old boy for alleged blasphemy in a school exam.

Police said the boy, Sami Ullah, was arrested under Pakistan's blasphemy law after authorities at his school in Karachi complained to police.

A police spokesman said he could not repeat what the boy had written on his examination paper because he himself would be committing blasphemy if he did.

Pakistan's blasphemy law allows for the death penalty for insulting Islam, although no one has been put to death.

Critics say the law is often used to settle scores and needs to be repealed or amended to prevent it from being abused.