The head of an Indian primary school where 23 children died after a meal made with contaminated oil has been arrested, nine days after she went into hiding.

Meena Kumari fled as soon as the children began falling ill after eating the lunch cooked at the school in Bihar state. Twenty-three children between the ages of five and 12 died and many others fell ill.

Forensic tests revealed that the food contained toxic levels of a deadly pesticide.

A police team investigating the deaths arrested Kumari and were questioning her to establish how the pesticide got mixed with the food.

Bihar's education minister, P.K. Sahi, has said the head bought the ingredients for the meal from a shop owned by her husband, who has also fled.

The school's cooks have told authorities that the head controlled the food for the government-provided free daily lunch.

One of the cooks said that the cooking oil appeared different than usual, but that the head told her to use it anyway.

India's midday meal plan is one of the world's biggest school nutrition programs. State governments have the freedom to decide on menus and timings of the meals, depending on local conditions and availability of food rations. It was first introduced in the 1960s in southern India, where it was seen as an incentive for poor parents to send their children to school.

Since then, the programme has been replicated across the country, covering some 120 million schoolchildren. It is part of an effort to address concerns about malnutrition, which the government says nearly half of all Indian children suffer from.