The low-intensity Agra blast appears to be a dry run for a possible terror attack on the third anniversary of the Batla House encounter, as the device was kept near a rather thinly crowded hospital reception area and far away from important places like the Taj Mahal.
The Uttar Pradesh anti-terrorism squad (ATS) fears Saturday's blast could be a rehearsal - like the recovery on May 25 of a device in a car in the Delhi high court car park, four months ahead of the September 7 blast at the court that killed 15 people.
A battery and wires found in the Agra blast site were similar to the battery recovered from the device found in May.
Indian Mujahideen operative Atif Ameen was killed in the Batla House encounter in New Delhi on September 19, 2008.
The Agra bomb, possibly kept in a steel tiffin box - a tell-tale sign of the IM - injured six persons.
It was a low powered device as it did not damage the fan above and only managed to crack the stone on which it was kept and shatter some windows.
Till late evening, the composition of the device was unclear and no timer or detonator had been recovered.
The explosion came at a time when the ATS was conducting a security check of important places in Agra, including Taj, due to a threat from IM remnants.