The Indian prime minister, Manmohan Singh, has promised that security forces will locate the culprits behind Wednesday's triple bomb attacks in Mumbai and bring them to justice.
No group has claimed responsibility for the attacks, which killed 18 people and wounded 131 others.
The blasts have soured the public against his government which undertook a highly publicised overhaul of domestic security after Pakistan-based fighters struck Mumbai in 2008, killing 166 people.
"The terrorists had the advantage of surprise," Singh said outside a hospital in Mumbai after meeting some of the injured on Thursday.
"This time there was no advance indication.
"Now our task is to find out who the culprits are and how we can work together to bring them to justice."
But Al Jazeera's Prerna Suri, reporting from Mumbai, said anger is mounting over the government's failure to prevent yet another series of attacks on India's financial capital.
P Chidambaram, the Indian interior minister, told the Reuters news agency it was too early to point the finger at a particular group.
The "co-ordinated terror attacks" could be retaliation for police action that led to a number of arrests and disrupted a plots, he said.
The lack of prior warning did not represent a failure by India's intelligence agencies, he said.
The home ministry said in a statement that police were interrogating members of a armed group, known as the Indian Mujahideen, who were arrested days before the attack, but that it had no specific leads on who
might be responsible.
"We live in the most troubled neighbourhood in the world. Pakistan and Afghanistan are the epicentre of terrorism," Chidambaram said.
He said Pakistan had still not given India support in pursuing those behind the 2008 attacks.
Source: Al Jazeera and agencies