Uttar Pradesh's minister for institutional finance Nand Kumar Gupta and three others were critically injured in a blast triggered by a remote-controlled device near his home on Monday morning.
Gupta was walking to a nearby temple when bombs placed on four two-wheelers went off. The other injured were his public relations officer, a security guard and an Indian Express journalist. All are in hospital.
While additional director general Brij Lal said in Lucknow that no arrests had been made, police in Allahabad said five aides of a local Samajwadi Party leader were picked up within a few hours of the attack.
Senior police officers said this was the first time such a device had been used to target a politician in the state. Bri Lal said teams of the special task force (STF) and anti-terrorist squad (ATS) had reached Allahabad.
Chief Minister Mayawati has sent principal secretary (home) Kunwar Fatehbahadur and DGP Karamvir Singh for a spot inspection.
IG Subesh Kumar said the blasts appeared to be simultaneous and a detonator and timer were used.
Their impact was so severe that all the four two-wheelers turned into a heap of scrap. Three of the two-wheelers belonged to persons known to the minister. Among them was a videographer who always accompanied him, said a senior police officer, wishing anonymity.
The police have fenced the area near Gupta's house.
The location of the house is such that his car is parked on the main road and he has to walk about 150 metres to reach home.
Asked whether the state government had any plans to review the security of ministers, Secretary (Home) Deepak Kumar said, "As of now, there are no plans.".
Lallu Lal Gupta, Gupta's close aide, said, "Gupta has no enemies."