Security at important public places and vital installations in Mumbai has been beefed up following an e-mail received by a news channel threatening a series of bomb blasts in the city.

Fifty-two people were killed in two blasts in Mumbai on August 25.

Also see: 45 minutes before the blasts, a warning

It's not known which militant group has sent the mail. It was received on September 22.

The mail warned of 'at least 100 blasts in the next 10 days.'

Mumbai Police Commissioner R S Sharma confirmed that the mail was forwarded to his department by the news channel. He said that although it appeared to be a prank, he is not taking any chances.

Sharma said the news channel received the mail on September 22 at 6:30 am in its feedback mailbox.

The cyber cell of the Mumbai police is trying to trace the origin of the mail.