Kolkata, March 25 (IANS): Only days after the gang rape of a nun in a convent in West Bengal's Ranaghat, a Christian missionary school in Jalpaiguri district has received a series of threat letters one of which even hinted at a replay of the Ranaghat crime.

The nuns of the St. Capitaneo Higher Secondary School for Girls at Champaguri in Nagrakata block received four threat letters between March 11 and March 21.

"A complaint was filed on March 22. We are investigating the matter," Jalpaiguri Superintendent of Police A. Rabindranath said. No one has been arrested so far.

The school - located around 600 km north of Kolkata - gives instructions in the Hindi medium, and the bulk of the 1,700 students are tribals.

With the furore over the March 14 rape of the 71-year-old sister superior of the Convent of Jesus and Mary in Ranaghat in Nadia district yet to die down, the administration has rushed police reinforcements.

Policemen have been posted in the school campus to prevent any trouble.

Inspector General of Police (North Bengal) Gyanwant Singh said: "We have taken the matter very seriously."

The school, near the India-Bhutan border, enrolls students from nursery to Class 12, with the residential section accommodating about 200 students.

The matter has already been brought to the notice of Chief Minister Mamata Banerjee, who has instructed police and the administration to take strong action.

The principal, Sister Anice Jacob, who lodged the police complaint, said classes were being held normally.