Bomb squads and police with dogs have spent the night combing the wrecked carriages searching for clues. Police have also carried out raids in the financial capital and surrounding areas, bringing suspects in for questioning, but no arrests have been made so far.

Medical teams worked throughout the night to treat the injured, but many anxious relatives are still making their way from hospital to hospital searching for loved ones. Train services in the city are almost back to full operation -- even the Western line, the target of the attacks, is creeping back to normal.

Suspicion quickly fell on Kashmiri militants after the blasts struck seven trains within minutes of each other on Tuesday.

But other Indian officials, speaking on the condition of anonymity, cautioned that it was too early to point fingers at a specific group.

One former senior intelligence official, Ajit Doval, said the blasts were too sophisticated for the Kashmiri groups to have carried out on their own.

"This is the work of groups which are targeting India as a whole and are not Kashmir specific and are pursuing the larger jihadi agenda," said Doval, who maintains strong contacts in the intelligence community. "They are targeting countries and societies, particularly democratic ones, which they consider to be the antithesis of their version of Islam."

So far, no one has claimed responsible for the attack, and two leading Kashmiri militant groups, Lashkar-e-Taiba and Hizb-ul-Mujahideen, have denied any role in the attack.