BALLIA (UTTAR PRADESH): Charges under the stringent National Security Act (NSA) have been slapped against the principal of a school in the Uttar Pradesh Board of Secondary Education's English question paper leak case, police said on Sunday.

Ubhaon police station SHO Avinash Singh said that the NSA has been invoked against Akshay Lal Yadav, the principal of Ma Lachhiyamurat Yadav Higher Secondary School.

Earlier, the NSA was invoked against three other accused in the paper leak case -- mastermind Nirbhay Narain Singh, Bhimpura Maharaji Devi Memorial Inter College manager Raju Prajapati and Ravindra Singh.

Police have so far arrested over 52 people, including three journalists, six school managers and five school principals, in connection with the leak of Class 12 English question paper on March 30. Ballia District Inspector Of Schools (DIOS) Brijesh Mishra is also among those arrested in the case. The three journalists arrested in the case were recently released on bail.