Bangalore, Apr 18 (IANS): Sleuths of the National Investigation Agency (NIA) and the city police crime branch Thursday intensified search for clues to the blast here a day earlier in which 16 people were injured.

"Our special teams are coordinating with the NIA investigators and forensic experts for vital clues from the blast site to ascertain the nature of explosives used in triggering the blast and who were behind it," a senior police official told IANS but declined to share details.

The blast took place near the office of Karnataka's ruling Bharatiya Janata Party (BJP) Wednesday morning.

Based on the evidence collected from the remnants of the gutted motorcycle and two cars from the blast site, forensic experts suspect chemicals like ammonium nitrate might have been used in the explosive and a timer to trigger it.

"We have got some leads from the preliminary investigation that point to use of a battery-operated timer device to trigger the explosion as we found remains of lithium and alkaline cells at the blast site," the official said.

As no shrapnel, nails or ball-bearings were found in the wreckage, experts doubt the use of improvised explosive device (IED) in the blast.

"We are also scanning the footage from the cameras and closed circuit television (CCTV) installed outside the BJP's state unit office to identify two persons who parked the motorbike between two cars and loitered before the incident. As the blast site is at a distance from the party office, the cameras could not capture the images clearly in the footage," the official pointed out.

Given that nobody was killed and injuries to the 11 policemen and five civilians were not major, sleuths are probing why the motorbike with the explosive was parked between the two cars, which bore the brunt of the blast.

"Impact of the blast would have been worst and even fatal if the motorbike was parked elsewhere. Luckily, there was no one inside the two gutted cars. The blast, however, was intense as evident from the extensive damage it caused in the area, including shattering of window panes and other objects in surrounding houses," the official observed.

Karnataka Chief Minister Jagadish Shettar also visited the blast site and held a meeting with top police officials, NIA sleuths and forensic experts for a first-hand account of the incident and the progress of the investigation.

"I have visited the blast site late Wednesday and earlier in the day to assess the damage caused by the bomb blast. As the probe is in progress, it would not be proper to make public the evidence collected so far as it may hamper investigation," Shettar told reporters after meeting some of the victims recovering in the state-run hospital.

The city police crime branch also rushed teams of five officials each to Andhra Pradesh and Tamil Nadu for additional clues. The ill-fated motorbike had a Tamil Nadu registration number.