Several persons were picked up for questioning in connection with Ahmedabad serial blasts and attempted blasts in Surat [Images] as a series of hoax calls, unclaimed objects and SMS threat messages kept security personnel on the edge on Friday.

Several activists of the banned Students Islamic Movement of India were detained in Ahmedabad [Images], Surat, Vadodra and Bharuch for questioning in connection with the bomb blasts that left 55 people killed and over 140 wounded.

"We have detained several SIMI [Images] workers from the city and their interrogation is in progress," said joint commissioner of police in Ahmedabad Ashish Bhatia. The city crime branch continued raids at various locations for the third consecutive day.

Ahmedabad crime branch officials said Abdul Halim, a SIMI activist who was arrested after the bomb blasts, has been remanded to police custody till August 10 and will undergo a lie-detector test. During his questioning, police found that he had links with Abdul Karim Tunda, a militant of the Lashkar-e-Tayiba, who is wanted for 1993 blasts in Mumbai            

Tunda, an expert in handling explosives, is believed to be in Pakistan, police officials said. He is wanted by police of various states for 33 cases of bomb blasts.

In New Delhi [Images], an anonymous letter threatening serial bomb blasts at Patiala House district courts complex in the afternoon was received by a magistrate court. Police tightened security arrangements in and around the complex which is frequented by thousands of litigants every day.

In Mumbai, an accountant from Ludhiana was arrested for allegedly sending a threatening e-mail. Deepak Pandey was nabbed on Thursday for allegedly sending an e-mail to a news channel in which he threatened more blasts. The e-mail was traced back to the Punjab city from where he was arrested, police said.

An unclaimed suitcase lying near entrance of Chennai Airport's international terminal created panic among passengers early on Friday morning before it was moved to a cooling pit by the bomb disposal squad. Bomb disposal experts opened it and found some clothes and an old watch. An anonymous letter was received by airport officials on Thursday threatening to bomb the airport if the Tamil Nadu government did not stop its newly-launched cable TV services.

In north Chennai, Bharathi Women's College recieved a call threatening that three bombs had been placed in the campus, challenging the police to prevent the explosions. The campus was searched for an hour but no explosives were found. The police said the call was made from a mobile phone and efforts were on to nab the prankster.

In Kozhikode, police control room got an SMS message -- reportedly from Pakistan -- warning of bomb blasts this month.

Kozhikode police commissioner Anoop Kuruvilla John said television channel Asianet's Chennai reporter Bimal Roy and Amrita TV's public relations officer in Thiruvananthapuram Rajesh got similar messages late on Thursday night.

The messages were reportedly sent from a Pakistani number asking to them contact KISH on a mobile number which had been traced to Kozhikode, John said. The message read 'Calicut blasts planned this month'.

A telephonic threat warning of bomb blasts in Kerala [Images] was received by a TV journalist in Bangalore earlier following which the state was put on high alert with security tightened.

Five suspected persons were also detained by the police near Siliguri.