Investigators today probed "every possible hostile group" in their search for culprits behind the Mumbai terror attack and the involvement of a suicide bomber was not being ruled out.

As Mumbaikars slowly came to grips with last evening's three serial blasts, no specific leads emerged and authorities did not want to speculate on who could be involved merely saying that "all angles" are being probed.

Union home minister P Chidambaram made it clear that it was too early "to point a finger at any one group".

All groups "hostile to India" are on the "radar" in the probe, he said. The Minister revised the death toll to 18 including a person with a severed head from 21 which was put out in an official list released by the ministry. 113 persons were injured of whom 23 are in a serious condition

Chidambaram rushed to Mumbai to review the situation and told reporters that ammonium nitrate, an explosive substance, was used in the Improvised Explosive Devices(IED) triggered by timer devices to carry out the "well coordinated" terror attack.

He also ruled out the use of remote control to trigger the blasts in Zaveri Bazar, Opera House and Dadar areas.

Union home secretary R K Singh did not rule out the involvement of a suicide bomber.

"The NSG DG has informed that a body with circuit has been found from one of the sites. The body was found near the explosion site. We are not ruling out anything," he told reporters in New Delhi.

Singh was replying to a question about the possibility of involvement of a suicide bomber in the blasts as the body was found with a circuit near one of the blast sites.

Maharashtra Anti-Terrorism Squad (ATS) chief Rakesh Maria said it was too early to say whether a "human bomb" was involved.

On the possibility of cross border linkages with yesterday's blasts, Secretary (Internal Security) in the Home Ministry U K Bansal said "As of now there is no ground to believe that there is any link of anyone from across the border."

Addressing a 70-minute joint news conference with Chief Minister Prithviraj Chavan, Chidambaram said "there was no "intelligence failure" on the part of central and state agencies to warn of an attack.

Asked whether the explosions were timed to disrupt the Indo-Pak Foreign Minister-level talks this month end, he said "we are not ruling out anything. That angle will also be kept in mind."

Maria said the ATS has taken over the investigations and the probe is not confined to any group.

CCTV footages from all the blast sites are being examined, he said, adding ATS has formed joint teams with the Crime Branch.

Bansal said there could be several reasons for the circuit to be found in the body of one of the victims raising suspicions whether the person could be a suicide bomber.

"One of the possibilities is that the person concerned might have been standing near the bomb and as a result some parts of the bomb imbibed it (body). There is another possibility that it could be planted in his body. But as of now we are not in a position to tell anything," he said.

Asked whether the body has been identified, he said since some of the bodies were found beyond recognisation, Mumbai Police was trying to identify them.

To a query on who could be behind the blasts, Bansal said as of now the investigators were not in a position to tell with confidence which militant group was involved in it.

"As of now there is no lead about any particular group. That is why we are probing into all angles and all groups are under radar and everyone is considered as a suspect. A few Indian Mujahideen militants arrested some time ago are being interrogated," he said.

"We are also looking into those groups which carried out similar blasts in the past. We are confident that some lead would emerge soon,? he said.

On the possibility of the involvement of underworld in the terror act since such groups were reportedly active in the metropolis in the recent past, Bansal said "all angles are being probed".

He also said there was no previous intelligence input about the blasts.

After his review meeting inMumbai, Chidamabaram said, "We are not ruling out any angle. We will probe (the involvement of) every terror group...The investigations into the attack will not start on pre-determined assumptions."

"Whoever perpetrated the attack has worked in a very very clandestine manner. Maybe it's a very small group, maybe they didn't communicate with each other," he said.

"I am confident that ... we will be able to zero in on the group that caused these bomb blasts," he added.

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ATS begins probe, registers three cases

Mumbai, Jul 14 (PTI) The Maharashtra anti- terrorism squad (ATS) today registered three cases in connection with the serial bombings that left 18 people dead and 131 injured.

"ATS has taken over the probe. Close to 12 joint teams of ATS and Crime Branch have been formed and we are being closely assisted by Central agencies. This case is being taken up on priority," ATS chief Rakesh Maria told reporters here.

Assuring people that no effort would be spared to bring the perpetrators of the latest terror strike to justice, he said, "We request the public to have faith and trust in the police. So far no (terror) case has gone undetected and the persons responsible for the blasts will be brought to book. We will get you the accused."

The maximum casualty in the last evening's terror attack was witnessed at Opera House where 10 people were killed. Seven persons died at the explosion at Zaveri Bazaar, the police officer said.

The third blast took place in Dadar.

"Samples have been taken from the blast sites.

Forensic experts are sifting through the debris for more evidence. It is too early to say anything regarding the kind of explosives used," he said, adding all angles will be probed.

The ATS chief requested people not to indulge in rumour mongering. "Even this morning there were rumours about six unexploded bombs being found in the city. We request people not to believe in such rumours and assist the administration in maintaining peace.