Indian investigators say attackers used a mixture of high explosives in last week's Mumbai train blasts that killed 182 people and wounded hundreds.
The head of an Anti-Terrorism Squad, K.P. Raghuvanshi said the explosive used was a mixture of ammonium nitrate, RDX and fuel oil. He declined to identify a group that may have carried out the attacks, saying only the investigation has reached a critical stage and has vital leads.
Investigators have said the seven coordinated bomb blasts on commuter trains in and near Mumbai bore the hallmarks of the Pakistan-based Kashmiri separatist group known as Lashkar-e-Toiba.
The group, which is fighting Indian rule in Kashmir, has denied involvement.
Meanwhile, Pakistan says India's postponement of scheduled talks this week is a "negative development" but voiced hope the dialogue between them will continue.
In Indian Kashmir, a top Kashmiri separatist leader urged the two nuclear rivals to continue the peace process. All Parties Hurriyat Conference leader Omar Farooq said if India pulls out of the talks now, it will help the elements who want to derail the peace process.
The bomb blasts on packed commuter trains in Mumbai triggered accusations by India that the attackers got support from militants inside Pakistan. Pakistan denies the charge and has condemned the attack.