After Surat, it's now Kolkata's turn to be on edge after an e-mail threatening bomb blasts on prominent streets and landmarks in the city.

Thorough searches late on Tuesday night did not lead to the recovery of any explosives. But police are not taking any chances.

Police have now detained a young man Kaushik Bose, the son of a cyber cafe owner in Kolkata's upmarket Salt Lake area.

Kaushik Bose was grilled through the night and the police have detained him for further questioning.

Police claims that that Kaushik has said he would help in identifying the people, who sent the threat e-mail from the cyber cafe.

The computer from which the e-mail was sent is in Kaushik's name. Police also said that the cyber cafe was operating illegally.