Patna, July 21: An initial forensic report has confirmed that the free school lunch that killed 23 children this week in Bihar was contaminated with a pesticide, a senior police official said on Saturday.

The children fell ill within minutes of eating a meal of rice and potato curry in their one-room school on Tuesday, vomiting and convulsing with agonising stomach cramps.

The deaths sparked protests in Bihar. The lunch was part of India's Mid-Day Meal Scheme that covers 120 million children and aims to tackle malnutrition and encourage school attendance.

It had already drawn widespread complaints over food safety. The report found the meal was prepared with cooking oil that contained monocrotophos, an organophosphorus compound that is used as an agricultural pesticide, Ravindra Kumar, a senior police official, told reporters.

Police said on Friday they suspected the oil was kept in a container previously used to store the pesticide. They are still looking for the headmistress of the school, who fled after the deaths.

The World Health Organisation describes monocrotophos as highly hazardous.