The Centre on Thursday described the near simultaneous explosions in Pune as a planned and coordinated act.
Union home secretary RK Singh said forensic experts were examining the two unexploded IEDs and nature of the four blasts.
"Since the blasts have taken place within an area of 500 metres and within a span of 45 minutes, it appears to be a coordinated act. I am sure there was a plan behind it," he told reporters in New Delhi.
Singh said teams of National Investigation Agency, National Security Guards and Central Forensic Science Laboratory reached Pune early this morning and were examining the explosives.
"They have examined two IEDs which had not exploded. There are three detonators in each and other peculiarity. Investigation is on. We are making progress," he said.
Home minister Sushilkumar Shinde said there was no update on the blasts so far.
Shinde, who assumed charge of the key department yesterday (Wednesday), held a high-level meeting with top home ministry oficials to review the security scenario in the country, particularly Pune, in view of last night's blasts.
On Thursday, Maharashtra home minister RR Patil said investigating agencies were probing all angles to determine whether any terror outfit was behind the low intensity serial bomb blasts that rocked the city on Wednesday night.
"Whether it was a terrorist act or not will be determined only after proper investigations are carried out by Maharashtra ATS, city crime branch and central agencies," Patil told reporters after visiting the four blast sites on JM Road in Pune.
Four coordinated low-intensity explosions struck the busy arterial J M road in the heart of Pune last night.
The explosions occurred at Jangli Maharaj(JM) road at spots near Balgandharva Theatre, Dena Bank branch, a McDonald food outlet and Garware Bridge.
Asked whether there could be a "saffron terror" angle to the incident, he said, "All angles are being probed and it will not be proper to comment at this stage."
Pune police suspects the role of at least three persons in planting the bombs outside McDonald's restaurant, Bal Gandharva theatre, Dena Bank and City shoes shop. One person identified as Dayanand Patil was injured in the blasts.
The man who was suspected to have carried one of the four bombs that exploded in Pune on Wednesday night and was injured has been identified as a local tailor, the city's Police Commissioner Gulab Rao Pol said.
The persons's name is Patil who is a local resident and working as a tailor in Junglee Maharaj Road, he said.
Pol said that "from the low-intensity blasts, we think there is no involvement of terrorist group. There may be other groups which are not related with terrorist activities", he said.
Asked about the possible motive behind the blasts, he said "the intention was to make mischief and create panic in the mind of the public".
A police officer at the site, requesting anonymity said, "The intensity of the blast was so low that it did not even pierce the dustbin in which the explosive was kept. The basket on the bicycles had a minor aberration. The bicycles did not even fall to the ground."
At 6.30 am on Thursday morning a team of the National Bomb Data Centre (NBDC) led by a lieutenant colonel visited the blast spot outside McDonald's restaurant on Jangli Maharaj road. The team collected samples of the explosive that that had gone off outside the restaurant.
Preliminary investigations reveal that the explosives contained ammonia and a sticky substance which was detonated using a detonator.
The entire Jangli Maharaj street, a plush locality in Pune, which was cordoned off till morning was later opened for traffic.