Mumbai: Investigators on Tuesday believed at least six newly recruited terrorists could have been involved in placing explosives in the triple bombings but there were no signs of a breakthrough in the probe nearly a week after the attack.

Maharashtra Anti Terrorism Squad(ATS), probing last Wednesday's Mumbai serial blasts, also suspect that the suspected attackers might have gone in pairs at the three sites--Opera House, Zaveri Bazar and Dadar--and that they have links with Gujarat and West Bengal. No organisation has so far claimed responsibility.

The death toll in the attack rose to 20 with one person, Ashok Bhata (45), succumbing to his injuries on Tuesday while undergoing treatment in a government hospital here.

"During our meetings with the various security agencies including NIA, there was an unanimous opinion that there could be at least six accused who must have been involved in the operation of placing the explosives at the (three) sites," an ATS official said.

They all must have been newly recruited in the terror outfit responsible for the blasts, the official said, adding they might have gone to the sites in pairs.

"We have a reason to believe that the terrorists could have strong links with Gujarat and Kolkata," the officer said but refused to divulge further details.

The nationwide hunt by the investigators was also intensified in an attempt to get some solid leads that could help them to nab the attackers.

The perpetrators of the blasts had kept explosives in a tiffin box at Zaveri Bazaar while the nature of metallic containers in which the bombs were kept at Dadar and Opera house is not yet clear, the official added.

The state ATS, Mumbai Crime Branch and National Investigating Agency(NIA) held a meeting that went on for several hours in which the progress of the case was reviewed
and investigation angles were discussed, the sources added.