Plain clothed police surround a vehicle which was damaged at the site of an explosion in the Dadar area of Mumbai July 13, 2011. Three explosions rocked crowded districts of India's financial capital of Mumbai during rush hour on Wednesday, killing at least eight people, media said. [Photo/Agencies]

MUMBAI, India - Indian police are looking into "every possible hostile group" in their search for the culprits behind the triple bombing in the heart of Mumbai that killed 17 people and wounded 131 others, the country's top security official said Thursday.

The attacks were the worst terror strike in the country since the siege of Mumbai that killed 166 people 31 months ago, and government officials struggled to reassure Indians over their safety.

"I want to assure everyone both in India and outside, that India will continue to work and grow and prosper," Home Minister Palaniappan Chidambaram said at a news conference Thursday after an emergency security meeting.

No one has claimed responsibility for Wednesday's bombings, which shook three separate neighborhoods within minutes of each other during the busy evening rush hour.

"We are not pointing a finger at this stage," Chidambaram said. "We have to look at every possible hostile group and find out whether they are behind the blast."

A steady morning drizzle washed away bloodstains and threatened evidence at the site of the attacks, which ripped off storefronts, shredded a bus stop and left bodies strewn in the dirt of Mumbai's crowded neighborhoods and market. Investigators covered the blast sites with plastic sheets to protect the evidence, police officer Shailesh Kadam said.

Shellshocked residents lambasted the government for failing to detect the plot, despite massive security measures taken after the attacks three years ago.

Chidambaram said Indian intelligence had received no warning of a possible attack on Mumbai before the blasts.

"Whoever has perpetrated this attack has worked in a very, very clandestine manner," he said.

The bomb in the Dadar area in central Mumbai was placed on a bus shelter; in the Opera House business district in southern Mumbai it was placed on the road; in the Jhaveri Bazaar jewelry market a few miles (kilometers) away it was on a motorcycle, Chidambaram said.

The bombs were made of ammonium nitrate and were not remotely triggered, he said.

Prime Minister Manmohan Singh condemned the blasts and appealed to the people of Mumbai "to remain calm and show a united face."

Pakistan's government expressed distress about the loss of lives and injuries soon after Wednesday's blasts were reported.