Five people have been detained in connection with the blast here that killed one man and critically injured five, including Uttar Pradesh minister, Mr Nand Gopal Gupta, police said on Tuesday, a day after the attack.
The five people are believed to be close to a local Samajwadi Party leader, on whose behest the blast could have taken place, a police official said.
The five were detained on Monday from the Naini industrial and the trans-Ganga areas following raids in several parts of Allahabad.
The blast took place in Mutthiiganj locality here when Mr Nand Gopal Gupta alias Nandi, the minister for finance (stamps and registrations), had stepped out of his home and was walking to a temple in the vicinity.
Mr Nandi, who was being treated in the Jeevan Jyoti hospital here, was late Monday flown in a state plane to the Sanjay Gandhi Post Graduate Medical Sciences (SGPGIMS), Lucknow, about 200 km away.
"The minister has been operated for his injuries," Arvind Baronia, one of the doctors treating Nandi, told reporters in Lucknow late Monday.
The 45-year-old man has been identified as Rakesh Malviya.
Police constable Sanjay, Nandi's security personnel Pritam, sweeper Shyam Babu and journalist Vijay Pratap Singh suffered serious wounds.
"They are all still undergoing treatment at a local hospital," Allahabad district magistrate, Mr Sanjay Prasad, told IANS.
While the minister was stated to be "out of danger", the condition of Vijay Pratap Singh and Sanjay continued to be "serious".
Uttar Pradesh's Anti-Terrorist Squad (ATS) and Special Task Force (STF) have been detailed to jointly probe the blast.
"We have to get to the bottom of this explosion and we will not leave any stone unturned to bring the culprits to book," Additional Director General of Police Brij Lal told reporters in Lucknow Monday evening.
Contradicting reports that it could be a low-intensity crude bomb, he said: "The intensity of the explosion could be gauged from the fact that three motorcycles parked along a wall were almost ripped apart while a moped went flying up in the air before falling a couple of metres away."
He did not rule out the possibility of a major conspiracy behind the whole affair.
While a forensic team was already on the job, Lal said: "The bomb could have been planted either in the moped or in one of the motorcycles."