The Detective Department of the Kolkata Police has started an investigation into the matter. The email was sent by persons who identified themselves to be belonging to an alleged terror outfit "Terrorizers 111".

"Hello, we are a Terrorist group called "Terrorizers 111". We must inform you, that we have placed multiple explosives devices inside your building....," the email said.

Tuesday's threat email was received less than a week after similar communications were sent twice to the city airport. Both the emails to the airport later turned out to be hoax.

Security has been beefed up in the state secretariat, Raj Bhavan and the Indian Museum.

According to the officer, the mail was also sent to senior government officials of other state governments and also those working in Parliament.

"We have beefed up security and an investigation has been started. But the mail like the earlier ones seems to be a hoax," the officer said, adding that they were in touch with the central government as well as other states' police departments.