A bomb that was defused may help reveal the nature of the explosives used in the Jaipur serial blasts on Tuesday night that killed 63 people and injured more than 153, police sources have said.

Till now, the police and other security agencies only know that the bombs were placed in brand new cycles, which they suspect were bought in Jaipur, and cycle-rickshaws.

"The police spotted an unclaimed bag in Chandpole, where one bomb had already gone off. They picked it up and it turned out to be a live bomb. The bomb disposal squad was called in immediately and they defused it on time. It is a low-to-medium intensity device and could have caused similar damage as that of the other blasts had it gone off," a police officer said.

"The timer was set for 8.45 pm and we recovered the bomb at 8.35," said a bomb disposal squad expert. Though they quickly disabled the timer, it took a team of bomb experts a full 90 minutes to defuse it, sources said.

The perpetrators had used ball bearings and a cheap alarm clock to assemble the bomb, which was placed in a satchel with only a piece of underwear to conceal the explosive, sources in the National Security Guards, which was rushed from New Delhi to assist the investigators, said.

Though reports quoting various agencies say that highly explosive material like TNT and RDX might have been used, the bomb disposal expert who analysed the recovered bomb said it is too early to say anything about the nature of the explosives. "What we could see was that a substantial quantity of pale yellow plastic was used in this bomb. We will have to wait to confirm whether any other explosive material was used in the other bombs," he said.

He also added that the defused bomb was put together with everyday material. "They had taken ball bearings and used surgical adhesive tapes to hold them in place. The timer device was a cheap small pocket alarm clock, which you get in any gift or stationery store."

The police added there was no similarity between the Ajmer and the Jaipur blasts. "However, we had seen the perpetrators use cycles in the blasts in Uttar Pradesh court premises. Similarly, ball-bearings and timer devices were used in the Hyderabad blasts," an officer said.