An email from the same Yahoo! account that was used to claim responsibility for the Jaipur blasts has triggered a security build-up of the kind Calcutta might not have seen before.

Police aren’t saying whether the email that landed in a top officer’s inbox last week is a new one from the Indian Mujaheedin or a forwarded copy of the one that was sent to the media to announce the “success” of its Jaipur operation and its plan for the four metros.

“The only information we have is that it is an email from that outfit. We have to take it seriously because it mentions our city as well,” a senior officer said.

The threatening email from guru_alhindi_jaipur@yahoo.co.uk prompted police commissioner Gautam Mohan Chakrabarti to convene a meeting of all senior officers on Monday and another with the heads of police stations on Tuesday.

The 48 police stations in the city were asked to compile tenant profiles in their areas of jurisdiction, gather details of visitors to all cyber cafes, visit hotels and lodges regularly and mobilise their retinue of informers to keep track of any suspicion-arousing activity.

Detective department chief Jawed Shamim and a colleague briefed the officers on how to insulate parking lots from terrorist activity and increase their intelligence base.

“The pattern of terror attacks keeps changing. An outfit that used ammonium nitrate in an explosion may use something else next time. We need to keep pace with them,” said an officer who attended the meeting.

The police have asked Calcutta Port Trust to install CCTVs on Howrah bridge and Metro Railway to beef up vigilance. New Market, chief minister Buddhadeb Bhattacharjee’s residence and Writers’ Buildings, too, will have electronic surveillance. The proposal has been forwarded to the home department and work is expected to begin in the next few weeks.

“While making a fresh analysis of the risk-prone zones, we realised that some of the possible target areas were not adequately covered in terms of surveillance. The list includes not only markets and offices, but also some intersections and places of worship,” a senior official had said last weekend.