Hyderabad, Feb 22: The bombs that went off at Dilsukhnagar here in the Andhra Pradesh capital Thursday evening, which killed at least 12 people and injured over 50 others, were kept on two bicycles, police said.

Director General of Police V. Dinesh Reddy said they were improvised explosive devices (IEDs) which were triggered with timers. He described them as "powerful blasts".

The terrorists were suspected to have used a mixture of Pentaerythritol tetranitrate (PETN) and ammonium nitrate in the blasts to cause maximum damage.

Unlike in the blasts in Pune, where the terrorists used new bicycles, they planted the bombs on old bicycles in Hyderabad.

Naga Sai, an officer in the bomb disposal squad, said they had not yet reached to any conclusion with regard to the nature of explosives.

He pointed out that unlike in the 2007 blasts, no splinters and balls were found at the blast site.

He said even a small quantity of explosives in a crowded place can cause a large number of casualties.

The officer also said terrorists did not keep distance or time between their targets.

"Both the places are close to each other and the second blast took place immediately after the first one."

Officials of the National Investigation Agency (NIA) and forensic experts were gathering clues at the blast scenes well past midnight.

They will be joined by more officials from NIA and post-blast team of elite National Security Guards (NSG) rushing here from New Delhi.