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The Associated Press
A policemen inspects the site of a bomb explosion at Zaveri bazaar in Mumbai, India, Wednesday, July 13, 2011. Three explosions rocked India's busy financial capital at rush-hour Wednesday, killing at least eight people and injuring 70 in what officials described as another terror strike on the city hit by militants nearly three years ago. (AP Photo)

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. The attack came just months after peace talks resumed between India and Pakistan. Indian officials have so far refused to speculate who might be behind the blasts.

"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 that New Delhi has blamed on Pakistan-based Islamist militants.

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.

Indian officials have accused Pakistan's powerful spy agency of helping coordinate and fund earlier attacks, including the 2008 Mumbai siege, which lasted three days. Peace talks between the countries were suspended after the siege and resumed only recently.

Asked whether the blasts might have been aimed at derailing the new peace talks, Chidambaram said: "We are ruling out no hypothesis."

President Barack Obama also condemned the "outrageous attacks." U.S. Secretary of State Hillary Rodham Clinton said she will go ahead with her plans to visit India next week despite the bombings. Standing with India "is more important than ever," she said.

Chidambaram lowered the casualty toll to 17 confirmed deaths and 131 injuries. He said a severed head was found that could be an 18th casualty. He did not explain the discrepancy from an earlier government statement that confirmed 21 deaths.

Associated Press writers Muneeza Naqvi, Ashok Sharma and Ravi Nessman in New Delhi and Kimberly Dozier in Washington contributed to this report.