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, which authorities said came without warning, were the worst terror strike in the country since the siege of Mumbai that killed 166 people 31 months ago, and government officials were struggling 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 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.

Meanwhile, families raced to find word about their relatives.

One man described hunting for information about his brother, who was in a jewelry market hit by a blast.

"We are in that market every day from morning to night," he told NDTV news channel, as he held back tears. "We went from hospital to hospital, and finally found his body in the morgue."

Kaushik Adhikari, 18, said his father, a goldsmith, was wounded in the same blast.

"He was hit by a shrapnel in the stomach and operated on. Doctors say he is stable," he said. "This has come as a big shock. We realize how uncertain life has become."

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.

"After the 2008 blast and all the media hype (about safety) we thought we were safe. But things still are the same and people in Mumbai continue to feel vulnerable," said Anita Ramaswami, a 33-year-old accountant.

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. Police were gathering evidence about the triggering or timing mechanism that set off the bombs and what types of containers they were in, Chidambaram said.

Surveillance cameras were in place at all three blast sites, Chidambaram said, but he did not reveal if any information was gleaned from them.

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 a new round of peace talks expected in a few days, Chidambaram said: "We are ruling out no hypothesis."

He also called for patience with the government's efforts to protect its citizens.

"We live in the most troubled neighborhood in the world," he said. "Pakistan-Afghanistan is the epicenter of terror ... living in the most troubled neighborhood, every part of India is vulnerable."

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. 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. Additionally, 131 were injured, 23 of them seriously.

As day broke Thursday, Mumbai began to return to normal life, with children holding umbrellas walking to their schools. Milk suppliers and vegetable vendors made rounds of the areas as municipal workers swept the streets.

Police and fire officers removed two dozen scooters and motorcycles from the jewelry market that were overturned and damaged by the impact of the powerful explosion.

The blasts marked the first major attack on Mumbai since 10 militants laid siege to the city for 60 hours in November 2008. That attack targeted two luxury hotels, a Jewish center and a busy train station.

C. Uday Bhaskar, a defense analyst, said the bombings showed that Mumbai remained vulnerable despite precautions taken after the 2008 attack.

"The local police still does not have either the capability or the capacity to pre-empt such attacks, and this is going to be a constant challenge," he said.

Last month, India and Pakistan held their first formal talks on the disputed region of Kashmir since the 2008 Mumbai attacks. Both nuclear-armed nations claim Kashmir in its entirety, and have fought two of their three wars over the region since they gained independence from Britain in 1947.

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