An explosive detected at Baroda Prestige Market in Varacha area, about 500 metres from Labeshwar Chowk where Modi had gone for first hand assessment, became the 21st to be defused in the city in the last three days.

It was similar to the 18 found on Tuesday from in and around Varacha, where several diamond processing units are located, they said.

Another bomb was found in Nana Varacha area. The bombs planted in Surat had integrated circuits, Deputy Director of Forensic Science Laboratories (FSL), Surat, S M Darji said.

"The detonators were attached to the battery and two wires were attached to the integrated circuit (IC). This means the circuit was complete and ready to explode," he said. Timer devices were used in Saturday's Ahmedabad blasts where 53 people have died and more than 140 were injured.

Finding no early breakthrough in the probe into the Ahmedabad serial blasts and the Surat attempts, Modi announced a reward of Rs 51 lakh for information leading to the terrorists involved in them.

With terrorists targeting cities like Bangalore, Ahmedabad, Jaipur, Mumbai and Hyderabad, their aim seemingly was to cripple financial activities in the country, he said.