"Special squads have been formed to find out who is behind the blasts. We have not got any conclusive leads yet," Bangalore's Additional Commissioner of Police M.R. Pujar told Reuters on Saturday.

India has suffered a wave of bombings in recent years, with targets ranging from mosques and Hindu temples to trains. It is unusual for any group to claim responsibility for attacks.

The home ministry said on Friday it suspected "a small militant group" was behind the attacks, but gave no details.

Some major IT companies in Bangalore, known as India's Silicon Valley, said they were increasing security at their offices after the eight low intensity bombs went off. Each bomb had a similar explosive force to one or two grenades.

The city is one of the world's most prominent centres for software development and is also home to a major outsourcing industry. "We have increased security in our campus," said a spokeswoman for Infosys, one of India's leading software companies.

Also nicknamed the "world's back office", Bangalore has more than 1,500 top firms, including Infosys, Wipro and the offices of global firms such as Microsoft Corp and Intel Corp.

"If such incidents continue, investors will fly away from the city," said state opposition politician Mallikharjuna Kharge, who called for improved security in the city.

Some police officials said they suspected the blasts could be the work of the banned Students Islamic Movement of India. "It is a prime suspect, but it is too early to come to any conclusion. All angles are being looked into," said a police official who did not want to be named.

Police said Friday's explosions were similar to a blast at a courthouse in Hubli, a city near Bangalore. Suspected Muslim militants there are being tried on charges of planning attacks in Karnataka, the state where Bangalore is located. No one was wounded in that blast.

Karnataka Chief Minister B.S. Yeddyurappa said the blasts were a conspiracy to defame his Hindu nationalist government. "We will not tolerate any attempt to spoil the reputation of the city" he said.