MUMBAI - Hundreds of investigators questioned suspects and scanned international telephone calls made after this week's deadly Mumbai blasts on Saturday.
Police sources said about 400 officers and men were involved in the mammoth hunt to find those behind the serial bombs that struck the Indian financial hub's commuter trains and stations, killing 179 people.
They were trying to find leads in several calls made to Pakistan, Afghanistan and Bangladesh from public booths, but so far not much headway has been made, the sources said.
No suspect has been officially named or arrested but hundreds of people have been questioned and dozens detained since Tuesday's explosions, which also wounded nearly 700 people.
"There are leads and they are being followed," police chief A.N. Roy said. "Investigations are following their own pace."
Indian newspapers and news television channels published photographs of two people they said were among three top suspects, but police denied having named anyone.
"There is a lot of speculation going around," Roy said. "Investigations have yet to reach a stage where we can draw conclusions."
However, police have made sketches of three other suspects seen at sites of the attacks, which hit crowded railway carriages and stations during the evening rush-hour.
Although there has been no breakthrough in the probe, Indian officials have said Pakistan-based Islamist militant group Lashkar-e-Taiba and Pakistan's Inter-Services Intelligence are the prime suspects.
Lashkar has long operated in troubled Indian-ruled Kashmir, but is believed to have expanded its area of operations recently.
The group has denied any role in the blasts, calling the attacks "inhuman and barbaric".
Prime Minister Manmohan Singh accused Pakistan on Friday of breaking its word by continuing to harbour Islamist extremists, and said peace talks with Islamabad would be threatened if it did not curb "terrorist" violence directed at India.
Pakistan has denied any involvement in the serial bombings.
In the meantime, survivors of the bombings, some of whom Singh met on Friday, have begun returning home from hospitals.
"We have begun releasing the patients in batches depending on the extent of their recovery," said Nilima Kshirsagar, dean of the King Edward Memorial Hospital, one of 12 hospitals treating the blast victims.
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