New Delhi, Dec 17 (IANS): A Delhi school principal was threatened over telephone a month after the school's official website was defaced by the Islamic State (IS) terrorist group, police said Wednesday.

Mohit Sharma, the 43-year-old principal of Raja Ram Mohan Roy senior secondary public school, filed a police complaint that he received a threat call from an unknown person on his office landline number Tuesday afternoon.

Sharma told IANS that the call was made just a month after the school's website was defaced by the IS, regarding which he has already registered a complaint.

Deputy Commissioner of Police Vikramjeet Singh told IANS: "The official website of Raja Ram Mohan Roy school was defaced by the IS. The case has been handed over to the cyber cell, but it is yet to confirm if it was a prank by anyone or the IS itself defaced the website."

Asked about the telephonic threat, the police official said they were investigating the matter.

The website was found defaced Nov 15.

Asked about the contents of the defaced web page, Sharma said some sentences were written in Arabic and some in English.

"We are proud of ISIS. We want all Muslims to be free. Muslims of Kashmir should be free. Islam is coming, don't worry," Sharma told IANS, quoting the content.

He said an IS flag was also put on the website.