Islamabad, May 17 (IANS): A school girl was killed and six others, including five students and a teacher, injured in firing inside a school in Pakistan's northwest Khyber Pakhtunkhwa province, police said.

A policeman deployed at the security of the school in Swat district opened fire at the children when they were returning home after attending classes, Divisional Police Officer of Swat Shafi Ullah Gandapur told media on Tuesday.

The nine-year-old girl's body and the injured were shifted to a nearby hospital, and two of the students were in critical condition, according to local media.

The suspect was arrested and an investigation was underway, he said, adding that apparently, the policeman had some psychological problems which made him commit the crime, Xinhua news agency reported.

Talking to police during the arrest, the culprit said that the firing was accidental and he did not intentionally target the children, school staff told media.