PATNA (AFP) - Police on Wednesday arrested the head of a school in eastern India where 23 students died after eating food contaminated with pesticide.

"The principal surrendered... and we have arrested her for questioning," said Mr Sujeet Kumar, police chief of Saran district in Bihar state where the children died.

"We need to talk to her first before framing charges," the official said by telephone.

The children, aged four to 12, died after eating a free lunch of lentils, potatoes and rice cooked at the school in a poverty-stricken village on July 16.

Oil used to cook the food contained an agricultural insecticide that was five times the strength sold in the market place, a forensic report found.

The head teacher fled and has been on the run since the incident in Gandaman village, which also left some 30 children ill in hospital and sparked angry protests.

Police raided the home of the head teacher last week where ingredients for the meal and cooking oil were kept, an officer has said.

Free lunches are offered to some 120 million school children throughout India in what is the world's largest school feeding programme.

Bihar is one of the country's poorest and most densely populated states.

Educators see the midday meal scheme as a way to increase school attendance. But children often suffer from food poisoning due to poor hygiene in kitchens and occasionally sub-standard food.