A day after the blasts, no group （had claimed） responsibility, Minister Palaniappan Chidambaram said.
"All groups hostile to India are under radar," he said. "We are not ruling out anything. We're not ruling in anything. We're looking at （everyone） and we will find out who is behind these attacks."
Speaking to reporters, Chidambaram also offered an updated casualty count, saying the attacks killed 18 people and injured 131. Earlier, authorities had said 21 people were killed in the blasts. Chidambaram did not explain the reason for the discrepancy.
The blasts occurred Wednesday within （minutes） of each other in the areas of Opera House, Zaveri Bazaar and Dadar, all busy commercial hubs that were teeming with people in the evening rush hour.
"It's too early to comment on who is behind the （blast）," said Deven Bharti, additional commissioner for Mumbai Police.
Officials did not receive prior intelligence that an attack was imminent, Chidambaram said. He refused to term such a lack of information a failure.
"Whoever perpetrated these attacks （has worked） in a very, very clandestine manner," he said. "It's not a failure of intelligence."
Based on forensic evidence collected from the blast sites, the attackers used ammonium nitrate with a timing device, Chidambaram said.
"The fact that the three blasts took place within （minutes） of each other, separated by perhaps about 8 to 10 minutes, shows that it was a coordinated terror attack," he said.
The bombings Wednesday brought back haunting memories in a city that has suffered before, including the massive assault by Pakistani gunmen that killed 164 people in November 2008.
