'Big power' behind train bombings

"It was a well-coordinated and well-planned operation and it seems some big power is behind all this," the police anti-terrorism squad chief K.P. Raghuvanshi told Headlines Today television channel.

The anti-terrorism force has taken over the inquiry and visited addresses across the city Wednesday but had not yet arrested anyone, a senior officer told AFP.

Forensic experts were examining timers found near the scene of the seven blasts, six of them in first-class compartments, that happened little more than 10 minutes apart.

The wreckage of the six carriages was taken to a railway shed where bomb squad officers continued to search them for clues, according to a railway official.

"It seems pencil timers, which are actually mercury fulminators, were used to carry out the blasts one after the other," a top official from Maharashtra state's home department told AFP. Mumbai is the state capital.

"We have collected some vital clues in this regard and the Central Forensic Laboratory has been requested to examine them without any delay," he added, on condition of anonymity.

Police said high-grade explosive material was used in the seven blasts during the evening rush hour Tuesday. Tests were being carried out but officers suspected the use of RDX or plastic explosives because of the power of the explosions.

Senior Mumbai police officer Arup Patnaik said he believed an eighth unexploded device had been found and added that anti-terrorist officers were now investigating. "I believe they have got some leads," he said.