An anonymous e-mail threatening to blow up the Bombay and National Stock Exchanges prompted the police to tighten security at the key buildings in Mumbai on Monday.

"An NSE official received the e-mail and I asked for security to be beefed up at the buildings immediately after being told about it," Joint Commissioner of Police (Law and Order) K L Prasad said.

Prasad said that teams from the Bomb Detection and Disposal Squad have been posted outside the National Stock Exchange building situated at the suburban Bandra-Kurla Complex and the Bombay Stock Exchange building in Fort, South Mumbai.

"Additionally, we have asked our men to sensitise the private security guards of the exchanges. Frisking will have to be very strong," Prasad said, adding that the police were trying to trace the origins of the e-mail.

The BSE building, one of the most prominent landmarks in the city, was one of the twelve targets of the serial bomb blasts in 1993. The BSE and the NSE have received bomb threat calls in the past also.

The latest threat comes on a day when the BSE Sensex zoomed by a whopping 640 points to breach the historic 19,000-mark.